education will, I fear, be a useless pastime; but whether that be so or not, I am certain that the accurate and neat representation of the elementary parts of machinery and buildings would be popular with the pupils and could be effectively taught. This kind of drawing educates band and mind in accuracy, it teaches the students the elements of mensuration and geometry, and it affords considerable scope for taste where taste exists. The chief difficulty will be to obtain competent teachers. I should occupy you too long were I to attempt to show how these must themselves be trained. My chief aim to-day has been to claim attention for a most important and wholly neglected branch of education. I shall probably be expected to urge the teaching of other natural sciences in our primary schools; nothing, indeed, would give me greater pleasure than to think this could be done. I confess I doubt it; while our second-grade schools are what they are in this respect, and while the Cambridge examination for a degree in applied science is what it is, I dare not think of natural-science classes in our primary schools. I shall be delighted if I am mistaken; but I am certain that mechanical drawing deserves our first attention, as most immediately useful to the artisan and most easily taught. The very books on natural science which are published in England cannot be properly illustrated for want of a sufficient number of competent draughtsmen; and children would be unable to follow the illustrations and diagrams if ignorant of the principles on which they are constructed. I look rather to good reading-books, explained by intelligent masters, as the best manner of teaching the elementary and all-important truths of natural science. No man could do better service than in compiling such reading-books, and there are few wants more urgent than that of masters competent to enlarge upon texts which would thus be put into their hands. The education of our workmen is far more incomplete than that of our professional men. Small additions to existing institutions will meet the want of the latter; but for the former the institutions have to be erected almost from the foundation. On an Apparatus for working Torpedoes. By PHILIP BRAHAM. The author of this paper described the various modes of working with torpedoes now extant, and explained their various disadvantages. He then explained his own, which was the propulsion of a torpedo from an invulnerable boat below its water-line by means of the expansion of compressed air. A drawing of the apparatus was exhibited by the author; it consisted of a compression-chamber, in which air could be confined to a great pressure, a tube through which the torpedo could be propelled, and a valve arrangement whereby the progressive velocity of the torpedo could be regulated. By means of machinery driven from the engines that move the ship he proposed to compress air into the compression-chamber to 500 lbs. to the square inch, and when within striking-distance of the vessel attacked the air to be suffered to escape behind the shaft of the torpedo, driving it with considerable force so as to strike the vessel attacked below its water-line and then to explode. By the reaction of the force driving the torpedo forwards, whose average statical pressure would be 85 tons on a diameter of 1-9 shown, the author expects the attacking boat would have its speed considerably diminished, if not entirely neutralized, and so prevent the possibility of collision. Account of some Experiments upon a "Carr's Disintegrator" at work at Messrs. Gibson and Walker's Flour-mills, Leith. By F. J. BRAMWELL, C.E. Carr's Disintegrator, as is probably well known to most mechanical engineers, consists essentially of two disks, each fixed upon a horizontal shaft. These shafts are placed in one line; the disks which they carry at their ends are separated the one from the other by a space of a few inches. Each disk carries a number of bars or studs disposed in several concentric rings, and standing out at right angles from its face. The concentric rings of studs of the one disk are arranged so as to be in the spaces between the concentric rings of the other disk. The disks are driven in opposite directions, and at a high velocity. The rings of studs, although very eye" numerous, do not reach to the centre of the machine; this part is unoccupied by studs, and acts as an 66 eye" to receive the feed. The first two or three rings of studs, beginning at the centre, are fixed to one of the disks only, viz. the one opposite to that through which the feed enters, and they serve to distribute that feed equably throughout the machine. So soon as the material has, however, passed by centrifugal force beyond the limit of the outermost of these central or rings, it is met by the first of the rings moving in the opposite direction. The studs of this ring find the material while in mid air and moving in a direction opposite to their own motion, and with a velocity due to the circumferential speed of the ring of studs the material has just quitted. The result of this meeting is clearly, first a violent blow, and then a reversal of motion, by which the whole of the material is sent flying through the air in a direction contrary to that which it last had, and with a velocity increased by the increased circumference of the ring of studs which has just put it into motion, a velocity and a direction, however, to be all but instantly arrested and reversed by the action of the next ring of studs, and so the material proceeds from ring to ring until it is delivered, completely pulverized, at the circumference of the machine. It will have been gathered from this description that a Carr's Disintegrator acts to reduce material upon a principle wholly different to those principles upon which millstones, edge-runners, crushing-rolls, rumblers, and stampers act; in fact, so far as the writer of this paper is aware, upon a principle which had never been applied to a similar or even to an analogous purpose, and that principle is the breaking up of the material by the action of a force which has no other abutment, if the term may be used, than the momentum of the material itself. In fact the material is treated as a shuttlecock, to be bandied backwards and forwards between mechanical battledores, suffering breakage at each blow until it is reduced to the required condition of pulverization. The proportions of the machine and the size of the spikes or studs are varied to suit the material to be operated upon. The particular machine upon which the experiments (the subject of this paper) were made is used for converting wheat into flour. It is about 7 feet diameter, and has a space of 10 inches between the faces of the two disks. The disk on the feed side carries six concentric rings of studs, which work between six concentric rings on the opposite disk. This opposite disk has also three "eye"-rings. The studs are circular, half an inch in diameter, and made of crucible steel. The distance from centre to centre of the studs is 2 inches, and from centre to centre of the rings also 2 inches, so that there is a clear space both circumferentially and radially of 2 inches between the studs. The revolving disks are enclosed in a casing, at the bottom of which there is an ordinary creeper or screw to convey away the meal produced; and as now very commonly applied to the cases of millstones, there is an exhaust-pipe connected with an exhaust-fan, to remove the dust and convey it to a depositing chamber, the "stive" room. The machine is driven from a counter shaft by means of two straps, one open, the other crossed, so as to give motion in opposite directions to the two disks. Their ordinary working speed is about 400 revolutions per minute. By the great courtesy of Messrs. Gibson and Walker, and with the able assistance of their engineer, Mr. Watson, the writer and Mr. Edward Easton were enabled to make the following experiments to test the power required to drive this machine under varying circumstances. In arranging the programme of these experiments, the writer was particularly desirous of ascertaining whether or not a suspicion he entertained as to a source of consumption of power in the working of the machine was justified by the facts. From a consideration of the number of times the disks revolve in a minute, and of the number of rings of studs, it is clear there must be many thousand settings into motion, and reversals of those motions, per minute of any material within the action of the disks; and it occurred to the writer that although the air within the zone of action of the machine weighed only between 30 and 40 ounces, yet even that trifling weight could not be subjected to such treatment without the consumption of a very considerable amount of power. He therefore determined to ascertain the power required, not only when the machine was working in its normal manner, both with and without feed, but also : the power when working without feed in an abnormal manner, viz. with both the disks revolving in the same direction and at equal speeds. The experiments and their results may be tabulated as follows:Power required to drive a Carr's 7-feet Disintegrator under different conditions at about 400 revolutions per minute. hour.... When converting into flour 20 quarters of wheat per Gross indicated horse-power. 145 123 63 19 From this Table it will be seen that when the machine is working abnormally, it only requires 19 horse-power to drive it, this power being employed in overcoming the friction of the journals &c., and in driving the disks while acting on the air, after the manner of an ordinary fan. Directly, however, the machine is put to work in its normal way, so as to deal with the air by repeated reversals, the power mounts up to 63-horse. It will also be seen that to make 15 quarters of wheat into flour requires 60 horse-power more than to work the machine when acting upon air alone, or at the rate of 20 horse-power for each 5 quarters of wheat, a rate that is very fairly corroborated by the increased power of 22 horses, as shown by the Table to be necessary when the feed is increased by 5 quarters, viz. from 15 to 20 quarters per hour. Further experiments were made with the object of ascertaining the power absorbed whilst running the machine empty at varying speeds. As this, however, could only be done by altering the revolutions of the steam-engine itself, there were practical difficulties attending the experiments which rendered any great range impossible, and also somewhat impaired the accuracy of those which could be made. The general result, however, showed that the power, as was expected, varied as the cubes of the speeds. Although it appeared, from the foregoing experiments, that the Carr's machine when running empty takes, in round numbers, 50 per cent. of the power used by it when at work upon 15 quarters of wheat per hour, it must not be supposed that it is an uneconomic machine as compared with mill-stones. On the contrary, both in power consumed and space occupied, the comparison is greatly in its favour. To grind 20 quarters of wheat per hour would require at least 20 pairs of 4 feet 6 millstones at work, and these would demand from 200 to 250 horse-power, and would occupy, including the necessary spare stones for dressing, about fifteen times as much space as the disintegrator. On this point of "dressing," Carr's machine possesses a further great advantage. With ordinary millstones one sixth of the number are always out of work for this purpose; and not only are they thus idle, but the wages of highly skilled stonedressers have to be paid. In the Disintegrator nothing analogous to "dressing" is required. The wearing parts are the studs; and judging from appearances, it would be many years before they require renewal. The machine from the principle of its action possessing this peculiarity, that a worn stud, so long as it is strong enough to beat the particles without sensibly yielding to them, will do its work just as well as when it was new. It would be beyond the scope of this paper to enter into the question of the relative qualities of the products of this machine and of ordinary millstones. It ought, however, to be stated that Mr. Gibson expressed himself to the writer as highly satisfied on this point. On a direct-acting Combined Steam and Hydraulic Crane. On the Rainfall of Scotland. By ALEXANDER BUCHAN, M.A., F.R.S.E. Secretary of the Scottish Meteorological Society. The paper was illustrated by a map of Scotland, showing the average annual rainfall at 290 places, many of the averages being from observations carried on through long series of years. The map brought out the large rainfall in the west as compared with the east-a difference which is strongly marked even in the group of the Orkney Islands. The average rainfall in the west, at stations removed from the influence of hills, is from about 36 to 40 inches; but in the east in similar situations the rainfall is as low as from 24 to 28 inches. In casting the eye towards the watershed of the country running north and south, it is seen that in ascending toward it from the west there occurs a rapid but by no means uniform increase, and in descending from it toward the east a rapid but by no means uniform decrease. The largest rainfalls occur almost wholly among the hills forming that part of the watershed of Scotland which is north of the Forth and Clyde. The places characterized by the heaviest annual rainfall are, so far as observation has yet enabled us to determine, the following:-Glencroe, 128 inches; Ardlui, head of Loch Lomond, 115 inches; Bridge of Orchy, 110 inches; Tyndrum, 104 inches; Glen Quoich, 102 inches; and Portree, 101 inches. At no great distance from several of these places the rainfall is by no means excessive, thus pointing out an enormous difference of climate between places not far apart. Along the watershed of that part of Scotland which lies south of the Forth and Clyde, no such excessive rainfall occurs, the highest being 71 inches at Ettrick Pen Top 2268 feet high. This diminished rainfall in the south, as compared with that at places further north similarly situated, is due to the mountains of Ireland draining the south-west winds of part of their moisture before they arrive at these parts of Great Britain. The distribution of the rainfall is very instructive in many districts, as in the valley of the Forth, from the head of Loch Katrine to North Berwick, where the amount varies from 91 to 24 inches; in Clydesdale, where the quantity is greatest at the head and foot of the valley respectively, being considerably less at intermediate places; and along Loch Linnhe and through the Caledonian Valley, where the variations of the rainfall are very great, and strikingly show the influence of purely physical causes, such as the configuration of the surface, in determining the amounts. In all these districts, as well as elsewhere, many cases might be referred to which conclusively prove that the amount of the rainfall is very far from being determined by mere height. In truth it is to local considerations we must chiefly look for an explanation of the mode in which rain is distributed over any district; and hence in estimating the rainfall, particularly of hilly districts, no dogmatic rule can be laid down. From observations which have been made at fifty places for lengthened periods, it appears that the deficiency of the three driest consecutive years' rainfall from the average, is generally from one fourth to one seventh, but that in some cases it is as great as one third and in others as small as one ninth. Since then the deficiency of the three years of greatest drought has varied from about 33 to 11 per cent.; it is evident, at least in so far as Scotland is concerned, that no dogmatic rule can be given stating a rate of deficiency applicable to all cases. If those districts were shaded off in which the rainfall does not exceed 30 inches annually, the great grain-producing district of Scotland would be indicated; and it is interesting to note that in those districts which produce the best wheat the rainfall is lower than elsewhere, being in many places as low as 24 inches annually. On the Rainfall of the Northern Hemisphere in July, as contrasted with that of January, with Remarks on Atmospheric Circulation. By ALEXANDER BUCHAN, M.A., F.R.S.E. On a new Mill for Disintegrating Wheat. By THOMAS CARR. In all previous mills and pulverizing machines the material operated on intervenes between, and is simultaneously in contact with two working surfaces. In this mill the disintegration is effected while the material is falling freely or being projected through the air unsupported, and no individual particle thereof, at the moment of disintegration, is ever in contact with more than one portion of the mill, viz. the particular beater striking and shattering it in mid air. It is also the only mill in which the projectile impetus in the material acted on contributes to its own disintegration. It consists of a series of beaters, formed of bars with open spaces between them, arranged cylindrically on disk-plates, around and parallel with a central axle. Into these disk-plates one end of each bar is rivetted, so that the bars stand at right angles to the faces of the disks, while their other ends are rivetted into rings, which so tie them that each bar is supported by the aggregate strength of the whole. These cylindrically arranged beaters (forming what may be called cages, from the slight resemblance they have to squirrel-cages) are of different diameters, so that when placed, as they are, concentrically one within the other, sufficient spaces may intervene between to isolate each, and give them the requisite clearance, and thus prevent any scrubbing or grinding-action on the material, which might ensue between them if they were rotating in too close proximity. These sets of beaters, of which for flour fourteen are used, are driven by means of an open and a crossed strap with extreme rapidity in contrary directions to one another, right and left alternately. The wheat flows in at the central orifice, and is thrown out by centrifugal force from the first cage at a tangent to its circle, and at a speed equivalent to that at which the beaters of the said cage are rotating, when, meeting the beaters of the next cage moving in an opposite direction, its direction is reversed, and it is again thrown outwards to meet the beaters of the third cage, also moving in a contrary direction, and so on with the other cages until (and that in less than a second from its first introduction) the fragments, reduced to fine flour, semolina, and bran, are delivered in a radiating shower alike from every part of the periphery into a surrounding casing, all the beaters (of which there are about 1000) being thus simultaneously effective, and the balance of the machine maintained. Thus, though with these different sets of beaters each acts independently, they are so arranged relatively to one another that not only is a repetition of the blows on the same material thereby obtained, as many times repeated as there are different sets of beaters, but the centrifugal force generated by the rotation of each set is caused to throw the material forward to the next set. Thus the first set of beaters throws it off and dashes it with great violence against the second, the second in like manner against the third, and so on in directions the reverse of that in which each successive set of beaters it strikes is moving, by which means the blows are enabled to act with redoubled energy on the separated particles of matter as they are discharged against them, precisely in the same way that stones are hurled from a sling. The machine can hardly be impaired by work further than the necessary wearing of the brasses of the four bearings. The crucible steel beaters, it is estimated, should last for ten years at least, and are then capable of being quickly replaced. It can pulverize easily 20 qrs. of wheat per hour, and dispense with twenty-five pairs of millstones. The percentage of flour from it is nearly the same as from millstones; but the quality of flour from the new mill is greatly superior, it being shattered into a fine granular state, not felled or killed as the bakers call it. The disintegrated flour absorbs more water, forms a raw paste of greater tenacity, and, when baked, a whiter, lighter, and much better keeping bread, with the sweet nutty flavour of the wheat most agreeably preserved. The cost of production of flour by this system is considerably less than by any other. Two of the machines have been successfully worked for many months at Messrs Gibson and Walker's Flour Mills, Bonnington, Edinburgh. |