No. 2 is the same machine with a powerful fore-jack in 8 itu, having twelve hooks or spindles. By means of this jack, and in conjunction with a suitable traveller or after-turn, twelve strands can be drawn out at one and the same time, and also four ropes up to 3in. or 4in. laid up at one operation.

The patent friction coupling, the principal details of which are shown in their relative positions as regards each other to the left of photo. No. 2, is an excellent appliance for communicating motion to machinery of this class, where the strains are so very irregular. The

IS SPACE VACUOUS?-AURORA. [869] SIR,-Will Mr. Barwiek (let. 773) state how

friction, are the essential parts of a combination for applying the power of the engine to the tightening of the ground-rope; when in situ it is arranged within the cast-iron foundation-box, and can be thrown in or out of gear instantaneously, thus effecting a great saving of time in this arduous operation. It is almost unnecessary to remark that the patent friction and this power-winding apparatus are merely placed in the position shown for the purpose of being photographed. The proper position of the friction is upon the main driving shaft, which communicates motion to the foreturn and the traveller. This communication can either be made through the medium of wheel work, or direct to the endless band, which, in the latter case, drives both machines. In either event the power-tightening apparatus is actuated by the endless band being Drought into contact with the ground pulley forming

part of the apparatus.

Your readers must note that the entire machine is raised upon blocks of wood for the purpose of being photographed, the latter having no connection whatever

with the arrangement.

The photographs being very clear and distinct, I have not considered it necessary to put in letters of reference.

In conclusion, I would remark that the object sought in this arrangement was to construct a machine, neat, compact, and portable, possessing the elements of simplicity, strength, and durability, and adapted, with the additional apparatus described, to the manufacture of ropes, from the smallest to the largest sizes, with the least possible expenditure of manual labour and of engine power, in all which points the machine has been eminently successful.

If acceptable I will shortly forward photos. and scription of an improved foreturn.

ISAAC WHITESMITH.

[868] SIR,-I find Professor Tyndall adopts the theory of a universally present ether in addition to the 63 elements chemists recognize along with heat, electric fluid, and luminosity. The learned Professor states (in "Heat a Mode of Motion," chap. xii.): "The natural philosophy of the future will certainly for the most part consist in the investigation of the relations subsisting between the ordinary matter of the universe and the wonderful ether in which this matter is immersed." I believe all hitherto-detected matter is atomic, with caloric and electric fluid excepted, as perhaps only a mode of motion." I take it this "ether" of natural philosophy, and the caloric of alchemy, and the fluid of electricity, when accounts are further balanced, will prove, if not one and the same thing differently conditioned, but diverse qualities of one and the same article; as we have flour and paper both fine, superfine, extra superfine, and coarse, as well as intermediate qualities and densities ad infinitum. But, as a student of chemistry, I can believe in no ether without an atomic constitution. I believe in the perfect vacuity of space exterior to solid bodies and their atmospheres, or there would be friction to the motion of planets, and that there is a fluid consisting of atoms far more minute than those of any of the recognized 63 elements, and that fluid the cause of heat and motion I deem extremely probable, and that fluid may be far better termed "caloric" than "ether." What is the motion or state of the thermometer in vacuo? Can heat be registered in an exhausted receiver placed in a hot oven or over the fire? I have not yet met with observations on this very important point, and would be glad to learn of any: they may be easily made. How can there be an "ether," in which "atoms and molecules swing," which is not itself held together by the attraction of its own atoms to each other? All atoms that combination with heat renders fluid or gaseous intermingle, at least in the case of air, radiatingly, and what is the "ether" that also intermingles but fluid caloric under another name? The hotter the gas, the more are atoms separated by additional fluid, yielding additional heat by radiation, and causing expansion wherever it reaches or resides. Less the calorie fluid, the denser the matter and the cooler. May not a very extreme minuteness in its atoms and a specific gravity quite inappreciable account for the penetrative power of heat-rays, to which the pores of densest solids are at once channels of easy passage and snug concealment ? Is it not the combustion force of this fluid penetrating minutest interstices that dislocates the atomic cohesion of molecules? Is not such a fluid (say "ether" if you choose) driven by com. bustive and radiating impulse, and caught and held by atomic attraction?

the two years the undertaking has been started. The manufacturers charge about 5s. quarterly. For this rent they find the apparatus with the necessary tap and tubings fixed at the place, and keep the filter in constant working order. For this trifling sum more than 200 gallons of water are daily purified in houses where the water is drawn from the cistern. cleaning of the same is included in the above charge. think a similar system started in London or any large town in England would prove a profitable undertaking, and at the same time be a great benefit for every SIDNEY GARDENER.

I

household.

17, Grasse Reichenstrasse,

Hamburg.

The

[871] SIR,-Thanks to your two correspondents for their replies to my query 5436 as to" applying and controlling power." I am still as far from what I require as before, for I find I omitted to mention that the machine is not intended to remain stationary, but may occasionally be upside down, &c., when a pendulum of any description would of course be out of the question. An escapement and balance wheel would answer, but I thought the ingenuity of some of your correspondents might suggest something more simple, as great accuracy is not required.

If you deem it worthy a corner in the MECHANIC I think I can give some of your subscribers a wrinkle as to gas bags. They are very expensive to buy, but the one I have made, according to the following directions, containing from 7 to 8 cubic feet, has not cost more than 12s. or 13s. I made it in the beginning of last winter, and it is now perfectly airtight, and answers my purpose admirably, better in fact than giving three or four pounds-as I should have to do-for one of similar capacity.

Buy from an india-rubber shopyard of the 6ft. wide waterproof (and airtight) sheeting, such as is used for children's cribs, i.e., that composed of two thicknesses of cloth with a layer of india-rubber between. The price should be 10s. per yard.

Place in an old saucepan gallon of that (asking your pardon for using so expressive a word) abominably stinking compound coal-tar naphtha. Add india-rubber (not vulcanized) cut into small pieces, until when thoroughly dissolved the solution is of the consistency of very thick paint. This may be expedited by placing the saucepan, well covered over, on a clear fire in the open air (to prevent accidents, as your sauce will be very inflammable).

with

Now, Mr. Editor, if you consider this only fit for your wastepaper basket, don't hesitate to put it there; I shall not be offended! but I should like to get a notion as to my regulator.

LIGHT AND HEAT.

P. R. W.

[872] SIR,-As it is an established fact that both light and heat are given off from every part of the visible spectrum, there arises in my mind a question concerning it, the answer to which seems to me rather puzzling. Given a certain point in the prismatic spectrum, say between the red and yellow portion, where the rays are all equally refrangible, and according to the undulatory theory emit waves of equal length, how is it that some of these waves produce heat and others light? I know it may be said that the same waves that, striking on the optic nerve, produce the sensation of light, may, by impinging on other nerves, produce heat; but there is a serious objection to this explanation, viz., if the rays, emanating as above described, pass through a solution of iodine in bisulphide of carbon, the rays or waves no longer produce light and heat, but heat only. Now, as they were assumed to be perfectly alike, how is it that some pass through and some are absorbed. curious fact will much oblige yours, An explanation of this to me S. P.

PNEUMATIC QUESTION (QY. 5302). [873] SIR,-Many thanks to your correspondents, Mr. T. Butcher, "O. F.," and "M. P.," for answering the above question; but I cannot help appealing to our princes of science, like Tyndall, "Sigma," &c., to refer the enclosed air in a sealed vessel can actually have the me to anyexperiment which has been made to prove that power of pressing against the internal sides at the rate of about 151b. per square inch when placed under the receiver of an air-pump where the air has been exhausted. It does not seem possible that a few grains of air under such circumstances, when separated from the external air, should prove as powerful in respect to pressure as if a column of external air to the extent of 50 miles above us, with all its weight, be brought to bear from the inside of the vessel, viz., 15lb. per square inch. This latter I understand to be atmospheric pressure, but I cannot understand how the expansive power of a few grains of air could be proved to equal the whole weight of the atmosphere.

If we accept "O. F.'s" theory to be correct, then I beg to throw out a second pneumatic question which I consider of great importance: how to counterbalance such internal pressure as under the circumstances mentioned.

I think it can be done by suspending a small vessel of metal, from which the air has previously been exhausted and closed air-tight, inside the air-containing bottle or vessel, before this latter is sealed and placed under the receiver of the air-pump; in this way I expect that the internal air of the original bottle will neither press against the sides of the glass bottle, nor against the suspended metal vessel. If any of your contributors possessing the necessary apparatus will give careful attention to my question and try the experiment, I shall then be able to state what great advantages could be derived from it. R. RHODES.

ELECTRICAL SUNDRIES.-FORCE. [874] SIR,-I have had suddenly thrown on me not only a heavy pressure of work, but work of that wearing character which unfits for work, and, therefore, if I am unable for a time to sustain the attention I have hitherto given to questions put to me, and delay somewhat the continuation of my papers on "Electricity" and other communications, I must ask your readers to remember that it is due to no failure of courtesy or diminished interest in "our" paper, but simply to other duties and to over-pressure alike on my time and mental powers.

I will reply here to a few questions hardly worth a specially localized answer.

(5550.) I should say the condenser should be made of sheets of foil 6in. by 5in. Twenty-five to sixty pairs, according to the battery power used.

(5553.) The cups of the sulphate of lead cell are tinned by the usual process of tinning copper, not with solder, though I do not think that would be injurious.

(5554.) Surely "J. S." hardly wants telling that when the battery fails in force its liquids should be replaced by fresh. If he only replaces the nitric acid then the consumption of the zine will go on at its expense, as he will see I explained in the papers on the various batteries in which an oxidizing agent is used at the negative element.

Mr. Tonkes's remarks on carbons (let. 803, p. 209) require some little emendation. He speaks of applying paraffine to the immersed surface. That would of course very greatly reduce conductivity, simply because it would prevent contact. If he refers to my instructions as to preparing carbons, p. 266 of last volume, to which I previously referred Mr. O'Connor, he will find the whole subject dealt with. The part to which paraffine is to be applied is the part which is not immersed. I have carbons thus prepared which have long done duty without the least deterioration, and I am satisfied (by careful experiment) that the conductivity of the carbon is not impaired by the saturation. I have, however, somewhat improved the process, and no longer heat the carbon, but put a piece of paraffine on it and apply a hot wire; its spreading is thus under better control. Thus treated, and the coppering carefully covered also, I have found no capillary action whatever, while there is perfect and continuous cirMr. Preston (let. 808, p. 210) seems to misapprehend what I said as to molecular forces, and specially of heat. My remark was not that we had no knowledge of the phenomena of latent heat or chemical heat, but that we knew nothing of the process of the phenomena. We do not at all know what is the nature of the motion, or how it passes from latent to sensible, &c., except that it does in some way change from a motion within the body, and not capable of passing out of it, to another motion which is transmissible to surrounding bodies.

cuit.

As to ventilation by steam jets, a very simple general principle has been overlooked. The steam has two actions. 1. Its actual heat, by which it acts as with any chimney. 2. Its mechanical force, which it imparts by "induction;" that is, really by friction against the particles of the air, &c., just as the flannel lifting water (see reply 5004). This can only produce an effect equivalent to itself. In an engine, or as in the case of D. Clarke's foundry, the resistance is small. The jet does much work, but in a coal-shaft the resistance and friction are so great that the mechanical force is much better applied by other means.

SIGMA.

UNEQUAL STEAM PRESSURE. [875] SIR,-Taking a great interest in anything connected with the working of steam engines, I have attentively perused the correspondence and diagrams of Inquirer," and replies of E. Malbon and W. W. B.," p. 205, and confess that the discrepancies between the statements of the two latter have only succeeded in making confusion worse confounded, the high pressure diagrams show an average pressure of useful work of 19-71b. For what reason "W. W. B." deducts the back pressure off it is more than I can tell. E. Malbon has evidently fell into the same error, for he says, No. 1 figure has front average pressure of 1611b., opposed by back pressure of 2141b. Now if this be true better by far take out the high-pressure cylinder and throw it in the old metal heap, as it only serves the purpose of offering a continuous resistance of 5lb. per square inch on the area of high-pressure piston. Happily for " Inquirer," it is not so. I always thought the effective work of a high-pressure diagram was the average pressure between the steam and exhaust line, and have not yet seen it proved to the conrary. The remainder of "E. M.'s" letter will evidently puzzle "Inquirer," as I don't think the latter had any idea of turning his exhaust from high-pressure cylinder into his turbine. Again the advice about lapping-valves and shortening rods given by any individual who has only diagrams and written statements to guide

easily see the companions of Rigel, Polaris, & Gemin., and 11 Aquile. It divides distinctly Pisc., Leo., & Serp., 2725, el and e2 Lyræ, 11 Monocerotis (triple, and 160 P. II.; also, with difficulty, e Bootis. The annular nebula 57 M is shown as a faint spot, darker in the centre than at the edges. Of course the fifth star of 01 Orionis cannot be seen with it. The power I generally use is certainly over 100.

ANALYSES OF MINERALS.

ALCOR.

[877] SIR,-Allow me to apologize to a "Collier Lad" for not answering his query before-in fact, I had a notion I had done so, until I saw, in the "Unanswered Queries" of your last impression, that I had omitted replying.

I am sorry a "Collier Lad" has no knowledge of chemistry; it would have been much easier to instruct if such had not been the case. He asks me to assist him; I will do it to the best of my ability. Procure Ward's "Chemistry," price 2s., and enter the nearest science class where chemistry is taught. After studying for at least a year, and obtaining a knowledge of the elements, their modes of combination, and the principal compounds which they form with one another, also a practical knowledge of the preparation of the gases, &c. (which may now be had at most science classes by a recent regulation of the Government), he may procure Macadam's "Practical Chemistry," which contains a list of apparatus and reagents, and is a very good work for a beginner. But a "Collier Lad" must not suppose that by pur. chasing and wading through a text-book of elementary analysis, that he will be able to analyze complex mixtures, such as minerals generally are; an enormous amount of work must be done, combined with a good general knowledge of chemistry, before minerals can be correctly analyzed; if, however, the most important constituents only are required, as the oxide in ironstone or lime in chalk, a less extensive knowledge is required. GEORGE E. DAVIS.

NACHET'S PRISM.

[878] SIR,-"Nachet's Prism" for drawing objects seen in the microscope after the manner of the camera lucida is not so well known in England as it deserves to be. I have found it of the greatest use, and have rejected in its favour all other contrivances for drawing from microscopic objects, and for the following reasons:-It has a good amount of light, fair definition, and the great advantage that in its use the ordinary inclined position of the microscope in observing is not interfered with; all that is needed, when it is wished to sketch some particular form, being to slide the spring ring which carries the prism on to the end of the eyepiece when the cap is removed, looking then as into a Wollaston prism, the object in the microunder the eyepiece. scope is seen as it were on the table, immediately The practical microscopist will recognize this as an enormous boon, as in all other drawing appliances known to me, the microscope has to be set horizontal, and in so doing the object it is wished to place on record is frequently displaced, if not lost altogether, and at all events much time is wasted in getting the illumination in a satisfactory state. This difficulty is particularly felt when a power of or is used. Experience will soon show that there is a particular angle (convenient for observation) for inclining the microscope, so that the prism shall perform at its best, but the inclination once determined need never be altered, and the temptation to sketch is very great when no change need be made in the posi tion of the microscope. (In practice I have an eyepiece with the prism always in position, so I only substitute the one eyepiece for the other.)

first to attempt a solution of the problems of the absolate amount of heat or cold conveyed by means of these agents, and the effect of this transference upon climate. His investigations have led to very wonderful results. Selecting the Gulf Stream as the best known, he shows by an apparently reliable chain of evidence that this current alone carries as much heat from the tropics as is received by the globe within sixty-three miles on each side of the equator-an amount which probably equals the entire quantity of heat received by the whole Arctic regions from the rays of the sun. Mr. Croll estimates that the stoppage of the Gulf Stream would deprive the Atlantic Ocean of a quantity of warmth equal to onefourth of all the heat received from the sun by that area; that if all currents ceased to flow, and each place were dependent upon the rays of the sun alone for its heat, the equator would be 55 warmer than at present, the poles 83 colder. The mean temperature of the latitude of London would be only 10. This city then, its present actual mean temperature being 50, is benefited to the extent of 40 of heat by the Gulf Stream. Basing upon Mr. Croll's estimate of the temperature (10) of the latitude of London if deprived of the warmth of the Gulf Stream, this seeming paradox must be true that an ice-bearing current may raise the temperature of a region. Labrador has really a warm friend in the icy current which clings to its shores, for though the mean annual temperature of that country is but 323, still, according to Mr. Croll's showing, this would be reduced by no less than 22° were the polar stream to fail. Though considerable uncertainty necessarily exists regarding the data used, yet the general results arrived at of the enormous influence of ocean currents on the climatic conditions of the globe in distributing the heat received from the sun cannot be materially affected, and almost warrant the conclusion come to by Mr. Croll that without ocean currents the earth would not be habitable. These discoveries appear to Mr. Croll to throw a new light on the mystery of geological climate. Were the warm currents from the equator northward to be turned off, the northern hemisphere would speedily pass into a state of general glaciation. Such a deflection of the carrents, it is believed, might take place by a change in the eccentricity of the earth's orbit. A high condition of eccentricity would tend to produce an accumulation of snow and ice in the hemisphere whose winters occur in aphelion, whilst exactly the opposite effect would take place in the other hemisphere which has its winter in perihelion. Then, since the trade winds owe their existence mainly to the difference of temperature which exists between the polar and the equatorial regions, it follows that the trade winds of this colder hemisphere would greatly exceed those of the warmer in strength; and would impel the warmer waters of the tropics entirely over into the opposite hemisphere, in the same manner as the south-east trade winds of the present state of the globe, from the southern (colder) hemisphere, now overcome in the northeastern, and aid in transferring a larger share of the equatorial waters to the warm currents of the northern hemisphere. A similar condition of things to that which prevailed during the glacial epoch would then exist in the one-half of the earth, whilst a climate equal to that which geologists know to have prevailed in this hemisphere during a part of the Miocene period, when North Greenland enjoyed a climate as mild as that of England at the present day, would reign in the opposite hemisphere." P. FRANCE.

SCIENCE A PEACE MAKER. one of the links which binds the human race together, [880] SIR,-The ENGLISH MECHANIC will prove and brings peace and goodwill to all workmen in every country where this paper is read; for this reason harsh and painful answers, such as Mr. W. B. Stanley gives in No. 294 (5386), should not be given, because it is

very cautiously acted upon. "Inquirer" cannot get the initial pressure of his boiler on the piston, if he has the ordinary slide valve to his cylinders, and governs with a throttle-valve, particularly if his workang-load is subject to fluctuations. From what I have learned from the correspondence respecting "Inquirer's" engine, I would say disconnect the highpressure cylinder altogether, use the low-pressure cylinder only; if worked with slide valve, put on a good expansion valve immediately behind it, with variable cut off motion in connection with governors; this will enable him to put on the initial pressure of the boiler on the piston, minus the loss from radiation, cut off at any part of the stroke required, and thereby reap all the advantages of steam expansion. This arrangement requires large capacity of cylinder, in proportion to indicated power of engine, in order to effectually reduce the terminal pressure of steam in cylinder to its lowest possible point. If "Inquirer" will state the indicated horse-power required by him the diameter of low-pressure cylinder, length of stroke, and number of revolutions, I might be able to tell him better if this arrangement would be more economical than his own. Say if 701b. pressure, means 70lb. above atmospheric pressure, or does it include the usual vacuum pressure of 15lb. LEH TEB.

THREE-INCH ACHROMATIC TELESCOPES. [876] SIR,-I am sorry to see so much in your correspondence columns to the disparagement of the cheap 3in. achromatic telescopes. I have one which, when stopped down to 24in. of aperture, shows an immense number of objects very satisfactorily. With it I can

The prism is difficult to sketch, but any body can easily cut its model in cork thus:-Cut a cube, and then take two slices off that cube, so that each slice shall be a triangular shape, with a central angle, and modified cube is the prism, and the square face, when the instrument is arranged, will be close to the near lens of the eyepiece and parallel to it; the prism to be looked through as though it were a Wollaston prism. I do not know if it is worth while mentioning that success in the use of all drawing prisms is got through a careful balancing of the light thrown on the drawing pencil, and that which comes through the microscope. I got my lens many years ago from Nachet, of Paris, and really thought it was identical with that known as the "Amici," but I find I was in error. However, now I have described the instrument I use, I am glad to be able to add that I find it as efficient with a 1-12th or a 1-16th objective as it is with a low power, and well worth having.

JOHN ANTHONY.

[Dr. Anthony has sent with his letter a prism, cut in cork, which we would gladly send to the first microscopist who asks for it.-ED.]

THE GULF STREAM.

[879] SIR,-To our numerous friends interested in what the Germans call Erd-gesetse, earth laws, or natural philosophy, the following, from the Academy, will afford considerable gratification and speculation :— "There is no longer any shadow of doubt as to the existence of a movement of warm water, be it called a drift or a stream, from the tropics obliquely across the Atlantic Ocean towards the Arctic regions. What end and purpose, then, does it serve, and what influence has it upon the condition of the globe? This question is ably answered by Mr. Croll, who, in the opening of a series of papers on Ocean Currents,' has been the

native of other countries; black sheeps are everywhere. no way inferior in intelligence and sobriety to any

SIDNEY GARDENER.

17, Grasse Reichenstrasse, Hamburg.

"E. L. G." ON THE MOON. [881]SIR,-I was aware that, as Mr. Proctor states (let. 812, p. 224), our astronomers have made sensible the effect of the earth's monthly displacement on the sun's transits, at the times of the moon's first and last quarters; but deny that this makes what I said (let. 771, p. 202) erroneous. I fail to see in it any proof that the same astronomers would, in the absence of any visible moon or visible cause for such displacement, have detected one eighty times as great, affecting no transit of the sun, but only his places at rising and setting. This is what the supposed lunarians would have to detect, with no clue, nor suggestion from other phenomena that their globe might be rotating round any axis away from her own; and I still believe the detection would require either greater instrumental means or cleverer astronomers than ours, who, if in their position, would most probably have yet to discover that the sun was more distant than 200 times their own globe's diameter. At present they are very peculiarly well placed for learning astronomy. I doubt if the solar system contains any spot where so much could be learnt, or a tenth so easily.

As for the possibility of Mr. Symons's lunar atmosphere, if, according to the stereoscopists, the known part of the lunar surface is part of so oblong a spheroid as to have its middle some fifty miles nearer to us than that of a hemispheric disc, the hidden side may

makers? Can any of your subscribers throw more light upon it? How is the vacuum produced, if that is the cause? M. PARIS

[884] SIR,-Perhaps as this question has been opened in your columns a few further remarks relative to it may not be inappropriate. They have been suggested by the fact mentioned in some late communications, viz., that the depths of many of the socalled craters or rings are generally small as compared with the widths. Schmidt, in his work "Der Mond," shows that the proportional depths decrease with an increase of the widths; and as this augments the difficulty of referring such rings to the effects of explosion may not the phenomena observed have resulted from, first, the expansion of an intumescent material below; second, an elevation of the superincumbent mass to the point at which tension and cohesion just balanced each other; and third, to the formation of fissures immediately upon the slightest increase of tension at the extreme boundary or boundaries of the elevated mass? William Hopkins, in his report on the "Geological Theories of Elevation and Earthquakes," printed in the volume of reports of the British Association for 1847, alludes to the elevation of land in this

It is driven by steam power, and the fast and loose pulleys are seen at the back part of the headstock, being a somewhat similar arrangement to a backgeared lathe. The large wheel on the mandrel is driven by a smaller fixed to the fast pulley, and the small wheel at the other end of mandrel actuates the feeding mechanism. The work is held in the parallelled vice which forms the top part of the compound slide-rest (at the right end of the machine), and it has also a vertical motion. R. M.

way, and its subsidence, with the production of a synclinal line between the two anticlinals on the boundary of the elevated mass. Adopting his theory of intumescent material existing within cavities of the earth's crust, and supposing such to exist or to have existed, within the lunar crust, the superficial boundaries or roofs of such cavities being more or less circular, we have the conditions necessary for the production of one of the largest craters, the character of the mountain wall being that of the anticlinals, as at a a, while the analogue of the synclinal is at the central portion 8. Hopkins suggests that in the almost momentary action of elevation and subsidence two systems of fissures are formed, those in connection with the anticlinals opening downwards as at a' a', and that in connection with the synclinal opening upwards as at 8. Scrope shows that lava does not ascend in the fissures opening downwards but is ejected from an opening produced in the upper part of the fissure opening upwards. There is, I apprehend, no difficulty in explaining the larger lunar rings on these principles, the central mountains partaking of the nature of volcanic cones. Scrope disposes of the convexity of Jorules by referring it to the distribution of ejected material from the cone. The convexity of Fracastorius may have been produced in the same way. These hints are merely thrown out as an inducement to your geological readers to bestow a tithe of their attention

on lunar matters, for he who would succeed in interpreting lunar phenomena should be well acquainted with those forces which have operated in breaking up and otherwise modifying the earth's crust.

The illustration is a section of Copernicus, a a being the opposite summits of the mountain border. From an observation of the earliest illumination of the floor

at b on Nov. 2, 1870, at 7.30, G. M. T., the interior ridged eastern slope occupies about one-third of the width of the crater, the breadth of the shadow of the western rim being at the same time 0-66; the ravines in the interior border of Copernicus may have possibly resulted from parallel fissures to those near the anticlinals.

Errata in my letter (685), No. 293, Nov. 4, 1870, p. 154, line 19 of letter, for "form a section" read "form a sector;" also line 24 (last but one), for "much marked " read "much masked."

ELECTRICAL SUNDRIES.

[885] SIR, Mr. Tonkes may be quite assured that he has not in the least incurred my displeasure (p. 226); the remark to which he refers was simply what it proclaims itself, a limit to the work I feel able to undertake in replying to queries put specially to me when they require the calculation of details. It is fortunate for "our" readers that Mr. Tonkes has returned to the ranks of the contributors, as I well know that he is equal to and disposed to deal with that very class of questions which I profess my own inability and disinclination to undertake. As Mr. Tonkes says, we have in the past had many a tilt, and I hope we shall have many more, and that in the friendliest spirit, each opening out the different views each mind takes, for while truth is one it is manysided.

"M.R.C.S.E." (let. 856, p. 233) misunderstands the term electro-motive force, which has nothing whatever to do with size of vessels, area of surfaces, &c. A cell made up of fine wires of copper and zinc would have exactly the same electro-motive force as one made of sheets a yard square, and would if opposed to it prevent any current passing from it. According to the best anthorities, the Grove has less electro-motive force than two Daniells in the ratio of 100 to 112.

The best reason which can be given why coal should not answer as well as carbon is that that obstinate old lady, Nature, will not allow it to be so. It is not a question of reason, but simply one of fact, and we might just as well ask why a sheet of glass will not answer.

AN IMPROVED MITRE BOX.

[886] SIR,-I send for the benefit of the carpenters and cabinetmakers of "our" journal the enclosed illustration of a recent improvement in mitre boxes, taken from the Scientific American. It is claimed to over come many of the objections heretofore met with in devices of this kind, with much saving of labour and accuracy in its working. It consists in an arrangement of adjustable stands and guides on a stationary bed, A, which may be made of either wood or metal, and of any desired length or breadth. To the opposite side edges of this bed are secured slotted cast metallic standards, B, which are made adjustable by means of the slot, C, and which work on the pivot, D. These standards have affixed to them strips of hard wood, between which the saw works in cutting mitres, bevels, &c.

E is an adjustable guide placed on the opposite lefthand corner from the work side of the box, and set exactly at right angles with the saw line. The purpose of this guide is to give a rest or guide for a piece like a casing for a window frame, when it is desired to cut

it to the bevel of the sill.

Upon the top of the bed are placed two adjustable mitre guides, F and G. These mitre guides consist of castings having slots, to which are affixed pieces of wood, in such a manner that either of the guides may be placed at the saw line, or run back out of the way of the piece to be cut from the other guide. It will be seen that by setting the guides, F and G, on an exact mitre with the saw line, H, and inclining in either direction the standards, B, a compound mitre or bevel may be cut of any desired form.

I is the working side of the box. In using this box, the saw, after having cut off a piece to any desired form, works down upon a strip of hard maple dovetailed across the bed. This strip can easily be taken out and replaced when worn. The strips of maple affixed to the standards, B, are adjustable to a saw of any thickness, and may be taken out, dressed up, and replaced when necessary.

No parts of this box, except the saw guides and dovetail strip, are destructible by reason of wear. In travelling from one place to another, it is easily packed and carried. The invention has been patented in America through the Scientific American Agency.

HOROLOGY.

C. A. J.

[887] SIR,-I find that query 4821, p. 622, has remained unanswered-and may I say, no wonder-for in that request by "Improver," we have no less than seven questions, to answer which would require three pages of the MECHANIC. I would urge all querists to make memoranda of their requests, but in no case in connection with horology to place before us more than two questions at one time. These questions by the above-named querist are so dissimilar that to answer them all at one time would (in my opinion) distract the mind from one subject to another, which I consider not a good way of imparting or receiving instruction. For instance, the first question is, "What is the usual method of determining and fixing the isochronism of a pendulum spring?" Next, the information required is concerning putting a pivot to a verge. Then follows the remaining five, to deal properly with which diagrams would be necessary. Hence some idea may be formed by "Improver" that my remarks at the head of this letter are somewhat reasonable. If "Improver" will refer to my transcript of Dr. Hooke's lecture on the "Pendulum Spring," he will discover that the study of that lecture will very much assist him in his inquiry on that subject. If he be in any difficulty concerning the practice, after he has understood the theory laid down in Hooke's lecture, I shall be pleased to assist him through the MECHANIC, but to answer him as it at present stands before us would require an essay, which would occupy more time than most journeymen-watchmakers can spare. I beg to inform "Improver" that I have practised in the ser

IMPROVED MITRE BOX.

vice of those who have paid ninety sovereigns to Possess themselves of that special part of watchmaking which is termed "springing and timing." I, therefore, wait for another request from "Improver" concerning " isochronism," after he has possessed himself of the theory of the pendulum-spring. Should he prefer any one of the other subjects to be replied to he had better write again. "Young Jobber" has forwarded a note to me for replies to five queries. The first, "What freedom is required for the wheels in pivoting in the pinions to a centre-seconds watch?" Hoping that he will read my remarks to "Improver," I say:-To an ordinary single train fourth-wheel centre-seconds movement, keep the fourth wheel low in the sink, but free; next insure the centre-wheel being free of it, but only just free, in order that the fusee may not be turned up too much to free the centre-wheel, because all that can be had as height of the fusee is necessary to insure a good chain. The next point to attend to is to keep the third wheel free of the fusee-cap, that wheel being reversed in its position. The pivoting in of the escapement requires merely the usual care for freedoms. Concerning the motion-work, that must be a subject for my next communication. The proper length for a fusee chain will be the following: When in such position upon the barrel as to be in the centre of the chain is fully wound up the barrel hook should be it, and as a general rule nearly lin. from the fusee cap when fully wound.

Jobber"

SECONDS PRACTICAL WATCHMAKER.

["Seconds Practical Watchmaker" says "Young has forwarded him a note for replies to five queries. We beg to repeat that we decidedly discourage private correspondence of this sort. We think that a contributor who is kind enough to send us information for the public good ought not to be taxed to write to individual correspondents. Many a man will cheerfully-as our columns abundantly testify-write down the results of his experience when he knows that what he says will be read by hundreds, perhaps by thousands; he may not, however, be so willing, as we frequently know from experience he is not, to devote the same amount of time and labour to satisfy a single person. Many of our ablest correspondents will not divulge their names; others who give their names do not add their addresses, and sometimes when they do we strike them out, to prevent the owners of them being written to by two or three, or it may be a dozen or more parties. We do our best to get the greatest amount of practical information for the largest number of inquirers, and with that we think our readers should endeavour to be satisfied.-ED.]

DISTILLED WATER.

[888] SIR,-The simple apparatus for distilling water, described on page 197, is a capital thing in its way, and answers the purpose admirably; but still it is imperfect. It is very easy to put on the fire, but how are you to take it off again? I have had one made, and am thoroughly satisfied; but instead of letting the tinman make it entirely, I bought a tin saucepan for the lower part, and then gave the tinman the job to make the upper; so now the apparatus has a handle to lift it from the fire with. Focus.

BIOLOGICAL.

[889] SIR, Mr. Jones's (let. 810, p. 210) controversy seems to be rather one of the definition of terms. What do we mean by food? All substances which are employed in the growth or in repairing the waste of the tissue of organisms? If so, air and water undoubtedly form a considerable part of our food. Water is required not only to build up the body of animals, but it acts as a solvent upon the materials taken into the stomach. So far from organic bodies being "permeated with comparatively little air and water," the case is just the reverse, and in the human

body the proportion of water to other material is 116 to 38. The principal, if not only, use of the oxygen we inspire, is undoubtedly to produce heat by burning tissue. Whether animals can act like plants in some cases and assimilate inorganic matter is still an open question. Are human beings heavier in the morning before they have touched food? The reason why men die sooner when deprived of water in cases of starvation is that the body principally consists of water, as water, and also that without water the tissues cannot be made to supply by their waste fuel for the oxygen of the air. I have never met with a case of a human being who M. PARIS. lived without solid food for weeks.

A PLEA FOR THE PRINTER. [890] SIR,-I have noticed from time to time in "our" journal that correspondents in correcting errata are apt to lay all the blame upon "your compositor." Now I think this is decidedly unfair. I acknowledge that compositors do make terrible blunders at times, but I do not think every fault can fairly be laid at their door. When we consider the various subjects connected with the "World of Science," and with which "our" journal is concerned, is it a matter of wonder that printers should not be "quite at home "in comprehending them? I presume the greater part of the

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very badly written; therefore I cannot think it out of copy" sent you is, like the general run of manuscript, place to remind our contributors that compositors are generally paid by the "piece." and that time wasted in deciphering caligraphy means so much less "breadand-butter," or, in other words, money. How many of our " readers are thoroughly acquainted with all the matters treated of in the ENGLISH MECHANIC? How can they imagine that printers understand everything? I have noticed during my time that technical terms, words and expressions exclusively connected with some particular trade, are invariably written raore illegibly than the common colloquial English. The late Lord Brougham wrote extensively on legal subjects. His manuscript presented the appearance of having been written with a skewer upon blotting paper, and when it is added that the longer words were generally contracted, the bewilderment of the printer may be better imagined than described. It was rumoured that, when the subject had passed from his memory, his lordship could not decipher his caligraphy himself. One other consideration may possibly weigh with your contributors. When an editor has so much valuable matter to choose from as you have, how can it be expected that he will waste his time in wading through illegible manuscripts, however bright the gold hidden by so much misplaced ink? SAUL RYMEA.

OUR "MOKE" AND THE EGYPTIANS. [891] SIR,-Before there can be said to be any evidence of a sensible variation in the length of the natural year, it must be shown that some ancient people reckoned time differently from the modes most natural, and certain to be adopted if the year had always its present length. Now this, I submit, has not been done. It was most natural (supposing the year of its present length) for men first to reckon twelve lunations, of 30 and 29 days alternately, making 855; and to eke out this by a thirteenth lunation when found necessary-namely, 7 times in 19 years, as the Jews and Chinese (the two most ostensibly conservative peoples on earth) do to this day-and as the Arabs declare their fathers to have done till the time of Mahomet. This is also the method evidently used in the first narrative employing exact dates to be found in any professedly historic document-namely, Noah's account of his Flood, as preserved and embodied by the compilers of the Hebrew Pentateuch, in Saul's reign.

But in that narrative (or perhaps pair of interwoven narratives, if Astruc's theory be adopted)-in that narrative, which I can produce many good confirmatory reasons for holding to be the most wonderfully accurate