hitherto prevented the employment of the air-manometer, and at the same time to be more accurate and unalterable in its working than the spring gauges now commonly used for steam-boilers. In the first place, it is a great defect in the common air-gauge that the divisions on the manometric tube diminish rapidly at high pressures, and consequently the reading becomes less and less accurate the higher the pressure. The new steam-gauge, on the contrary, possesses the same degree of accuracy at all pressures, and even enables us to make the accuracy of reading greater at higher pressures. Another serious defect of the air-manometer is the liability to rupture of the narrow column of mercury when the steam is suddenly shut off or turned on. This is entirely avoided in the present instrument by the use of two closed vessels communicating with each other only by very narrow capillary tubes. Finally, the small column of mercury enclosed in the glass tube of common air-manometers is subject to capillary depression, and to the disturbing effects of heat upon the airbulb and upon the mercury. In the instrument now to be described it is sought to avoid these defects by not using capillary tubes for the manometer, and by disposing the air and mercury in such a way as to make the effect of heat insensible. The air-tube of the manometer consists of a series of tubes of equal length, but different diameters, joined together by means of a blowpipe, and ending at the top in a glass bulb. The lower end is connected by an air-tight screw, joined with the first of two iron vessels containing each mercury or some other liquid, and communicating only by a very narrow capillary tube or channel. The manometric tube is sealed at the bottom, but there are two fine capillary openings through the side at points below the surface of the mercury or other liquid contained in the two iron vessels. Hence the communication of pressure from the steam or other compressed gas, whose pressure is to be measured, and which presses directly upon the surface of the liquid in the second iron vessel, can only take place through a system of two capillary channels; and the resistance which these channels oppose to the motion of the mercury, by which they are filled, makes it impossible for sudden changes to occur in the height of the manometric column, and thus entirely prevents the division of the column or the entry of steam or gas into the manometer. The capacities of the tubes and of the globe, which compose the manometric tubes, are so adjusted that they decrease in the same ratio in which the pressure increases, which is evidently what is required by Mariotte's law in order that an increase of pressure of one atmosphere may cause the first tube to be filled by the enclosing liquid, and that a further increase of pressure of the same amount may cause the second tube to be filled, and so on, each equal increment of pressure causing the same rise of the liquid in the manometric tube. This adjustment of the capacities is effected as follows:-Let the capacity of a manometer, to be divided so as to show pressures up to, say, four atmospheres, be called unity, and let v1, v2, v3, and v be the capacities of the first, second, and third tube and of the terminal globe respectively, then we have— This gives for the capacities of the tubes and their radii : where h is the length of each tube. To prevent accidental breakage of the manometer, it is fastened to the graduated brass plate, and with it screwed to a glass cover of an inch thick, capable of supporting a pressure of 20 atmospheres. ELECTRICITY AND MAGNETISM. On the Influence of Clean and Unclean Surfaces in Voltaic Action. 1. Gas was evolved by the contact of zinc and platinum surfaces, then an equal amount from the same surfaces when the platinum had been cleaned by hot oil of vitriol; the time was exactly half when the clean surfaces were used; contact of the surfaces with the fingers or dipping them in solutions of various substances was found to retard the evolution in a very marked degree. 2. Heating the platinum in a measure cleaned it, but not so satisfactorily as hot oil of vitriol. Copper and other metals behaved similarly to platinum. 3. Platinized silver, from its method of manufacture, appeared to be already clean, no advantage being obtained by chemically cleaning it. 4. Mechanically roughened surfaces of platinum exhibited a decided advantage over smooth ones. 5. The cell of a Smee's battery, examined by a galvanometer, gave vastly better results when the negative plate had been chemically cleaned. 6. Voltameters, the plates of which had been chemically cleaned, exhibited a marked superiority over those not so cleaned; thus it appears that in all voltaic action the results are superior where the surfaces of the negative metals, electrodes, &c. have been chemically cleaned, and that mere contact with the finger is sufficient to modify the evolution of gases from the surface. On a new Form of Constant Galvanic Battery. By LATIMER CLARK, C.E. (Extracted from a Letter to Sir William Thomson.) I have spoken to you several times about a form of battery which can be set up under such conditions as to ensure uniformity of tension within limits of about 05 or '06 per cent., and that without any special precautions as to the purity of the materials employed. I have not yet been able to make the necessary experiments for determining its value in absolute units, though I hope shortly to have made an independent determination. I have, however, set up about 200 of the elements in question, and have measured them on about 30 different days; and from the mean of these experiments, taking the Daniell at 1.079 volts, I make this element to be 1.403 volts. In obtaining this result I have had to make careful measurements of electromotive force of more than 1000 different elements, comprising some 40 or 50 different kinds; in fact I have been working at it for six years. The element in question varies about 07 per cent. for each degree Centigrade, getting weaker with increased temperature: the temperature at which our comparison with the Daniell's cell is made is 18° Centigrade. The element consists of a cylinder of pure zinc resting on a paste of protosulphate of mercury and saturated solution of sulphate of zinc, previously boiled to expel the air, the other electrode being metallic mercury, connexion being made with the latter by a platinum wire. It is desirable that the materials should be pure; but if commercial materials be employed the error does not exceed '06 per cent. at first, and after three or four hours the value becomes sensibly the same as with pure materials. The precautions necessary are that the protosulphate of mercury should be free from persulphate, and that the solution of persulphate of zinc should be supersaturated. The elements do not vary sensibly for two or three months, say '05 per cent. It is essential that the element should not be worked through small interpolar resistance; but the measurement should be made by the use of a condenser, or, infinitely better, by my "Potentiometer," which, with a Thomson's reflecting galvanometer, readily measures to the millionth part of a Daniell's cell, or very much less if required. Notice of and Observations with a New Dip-circle. By J. P. JOULE, LL.D., F.R.S., &c. The method of suspension of the needle, which formed the principal feature of the new instrument, was explained. The increased facilities of observation had enabled the author to trace the diurnal variation of inclination with greater accuracy than he believed had hitherto been done. At Manchester, about the summer solstice, the greatest inclination was found to occur at 21h 40m local time, and the range extended to 5'. The simultaneous variation of horizontal intensity was such as to indicate that the total intensity was very nearly a constant quantity. On Thermo-electricity. By Professor TAIT. It results from Thomson's investigations, founded on the beautiful discoveries of Peltier and Cumming, that the graphic representation of the electromotive force of a thermo-electric circuit, in terms of temperatures as abscissæ, is a curve symmetrical about a vertical axis. This I have found to be, within the limits of experimental error, a parabola in each one of a very extensive series of investigations which I have made with wires of every metal I could procure. To verify this result with great exactness, and at the same time to extend the trial to temperatures beyond the range of a mercurial thermometer, I made a graphic representation, in which the abscisse were the successive indications of one circuit, the ordinates those of another, the temperatures being the same in both. It is easy to see that if the separate circuits give parabolas (as above) in terms of temperature, this process also should lead to a parabola, the axis, however, being no longer vertical. This severe test was well borne, even to temperatures approaching a dull red heat. Unfortunately, it is difficult to procure wires of the more infusible metals, with the exception of platinum and palladium, so that I have not yet been able to push this test to very high temperatures. I hope, however, with the kind assistance of M. H. Sainte-Claire Deville, to have wires of nickel and cobalt, with which to test the parabolic law through a very wide range. Parabolas being similar figures, it is easy to adjust the resistances in any two circuits so as to make their parabolas (in terms of temperature) equal. When this is done, if the neutral points be different, it is obvious that by making them act in opposite directions on a differential galvanometer we shall have deflections directly proportional to the temperature-differences of the junctions. It is a curious result of this investigation, that, supposing the parabolic law to be true, the Peltier effect is also expressed by a parabolic function of temperature, vanishing at absolute zero. I was led to this inquiry by a hypothetical application of the Dissipation of Energy to what Thomson calls the electric convection of heat, and my result is verified (within the range of my experiments), that the specific heat of electricity is directly proportional to the absolute temperature. It is scarcely necessary to point out that the above results appear to promise a very simple solution of the problem of measuring high temperatures, such as those of furnaces, the meltingpoints of rocks, &c. On a Method of Testing Submerged Electric Cables. By C. F. VARLEY. On a New Key for the Morse Printing Telegraph. By CH. V. ZENGER, Professor of Natural Philosophy at the Polytechnic School in Prague. I had devised in 1868 a new automatic key to work the Morse telegraph. It produced three marks, viz. a point, a short line, and a long line. It con sisted of three levers; by pressing them down steel springs moved along a very short, or along longer sheets of conducting material, and formed thus three signs of different lengths. Yet there was a certain time required to work the three keys; to obviate it, and to put the telegraphist entirely at his ease as to the speed attainable for him, and to obtain in such a manner the highest speed possible, I constructed the key in another manner. A clockwork arrangement moves a small wooden cylinder, whose steel axis is attached to it by a handle, and rotates with great velocity, the rate of velocity being accurately indicated by sounding a small bell as often in a second as the cylinder will revolve in the same time. The wooden cylinder bears three thin circular disks of brass attached to the steel axis of the cylinder; these disks are differently cut out, in such a manner that the first is a full circle of 360°, the second a sector of nearly 120°, the rest of the circle being covered with an insulating material, viz. wood or india-rubber, to prevent metallic contact. The third disk is only a segment of 10°, the rest being cut out and covered with the insulating material. Three levers, put in front of the three disks, bear on their ends platinum wires or plates that touch the disks during one revolution of the cylinder when pressed down. From the levers a conducting-plate, uniting them, leads to the printing apparatus, and the levers are reduced to their former position by strong steel springs, so that they regain rapidly their positions after the pressure of the finger has ceased. Whatever be the velocity of the paper and the rollers, and the clockwork moving it, the relative length of the sizes and their distances remain unalterably the same. In the model presented to the General Post Office, the motion endures for 15 minutes, and, being only a model, it is worked by a spring, and it has no rollers for the paper. In the working apparatus for telegraphic use, the rollers and whole printing apparatus are attached to the key, and the same clockwork moves both the rollers and the rotating cylinder, forming thus only one apparatus together. From that contrivance we obtain : 1. A quite equal distance between the signs, as in printing. 2. By putting the fans of the clockwork in differently inclined positions, the velocity may be carried to as great an extent as a clever clerk can manage it. 3. By using three signs instead of two, the signs for letters, figures, and phrases are reduced about one-third, and as much of time and space is spared. METEOROLOGY. On the Importance of the Azores as a Meteorological Station. In this paper the author classed his remarks under three heads :-(1) as to the importance of the station; (2) as to the present condition of the question of its establishment; (3) what remains to be done. He showed that, although we have very copious results of observations made by vessels crossing the various oceans in all directions, there is great deficiency of actual observations at fired points. After pointing out the very important position occupied by the Azores, as illustrated by the researches of Mr. Buchan and Prof. Mohn with reference to the normal tracks of European storms, and also in their lying so completely in the path of merchant vessels, Dr. Ballot explained that about five years ago he submitted to the British Admiralty a proposal for establishing a chain of barometric stations in the S. and W. of the British Isles, and at the Azores, and obtaining meteorological reports from thence. In April 1866 he applied to the Portuguese Government and to various learned meteorologists; and the Director of the Lisbon Observatory has been to Holland to consult Dr. Ballot on the subject. A concession has been granted for the laying of a cable to the Azores; a learned 1871. 4 Portuguese has undertaken to provide the instruments and instruct the observer. The only expense involved is the charge for the transmission of the telegraphmessages: it would be most unfair that a country like Portugal should bear all the cost (about £350 per annum for one message daily); and Dr. Ballot thinks that it should be raised jointly and proportionally by the European Maritime States, all of whom would largely benefit by the adoption of the proposal. Mean Temperature of Arbroath. Latitude 56° 33′ 35" North, Longitude 2° 35′ 30′′ W. of Greenwich. By ALEXANDER BROwn, LL.D. April May June ... 1867. 1868. 1869. 1870. 4 13 22 26 years. years. years. years. years. years. years. -13 -3.3 January 330 413 410 364 379 37.5 364 366-04 ... ... 397-03-05 -0.5 443 +05-37-32 49'2 0.0-0.5 -0.5 554-04-10 −0·9 58.3-10-11 -1°0 572 574-10-14-12 534 536-09-18-16 468 469 +01-04-03 404 405-06-10-09 379 379 +12 +03 +0.3 Means...... 467 489 476 474 476 470 463 464-06-13 | — 1°2 of The author constructed from his meteorological journals the foregoing Table for the purpose of showing the Mean Annual Temperature at Arbroath, in the county of Forfar, on the east coast of Scotland. In the Table, columns nos. 1, 2, 3, and 4 give the monthly mean temperature, and also the annual mean temperature, each of the years 1867, 1868, 1869, and 1870. The warmest of these four years was 1868, and the coldest the year immediately preceding, namely 1867. The mean temperature of 1868, as shown by the Table, was 489, and that of 1867 46°-7, the difference between the warmest and coldest year of the four being 2°.2. Column 5 is the mean of the monthly and annual temperature of the four years already mentioned; column 6 is the mean of 13 years, from 1857 to 1869 inclusive; column 7 is the mean of 22 years, from 1845 to 1866 inclusive; and column 8 is the mean of 26 years, from 1845 to 1870 inclusive. The annual mean temperature of the 4-year period is 47°6, of the 13-year period 47°0, of the 22-year period 46°3, and of the 26-year period 46°.4. It will be observed that the annual means of the two long periods differ by only one tenth of a degree, and are therefore a near approximation to the mean temperature of the locality. The thermometers used are the Minimum thermometer of Rutherford and the Maximum thermometer of Negretti and Zambra, which have been tested by the Standard instruments of the Scottish Meteorological Society. They are attached to a wooden frame fixed to a window-sill having a northern exposure. Very great care is taken to protect the instruments from the effects of radiation and other causes. The thermometers are placed 11 feet from the ground and 70 feet above the level of the sea, and distant therefrom 783 yards in a direct line. |