to elicit an opinion whether the results likely to be obtained would be of sufficient importance to warrant a more elaborate discussion of the entire series of observations with a view to future publication.

Poste Photographique. By the ABBÉ MOIGNO.

An Account of a New Photographic Dry Process. By R. SUTTON.

HEAT.

Description of Experiments made in the Physical Laboratory of the University of Glasgow to determine the Surface Conductivity for Heat of a Copper Ball. By DONALD M FARLANE.

The experiments described in this paper were made under the direction of Sir W. Thomson during the summers of 1865 and 1871. A hot copper ball, having a thermoelectric junction at its centre, was suspended in the interior of a closed space kept at a constant temperature of about 16° Cent., the other junction was kept at the temperature of the envelope, the circuit was completed through a mirror galvanometer, and the deflections noted at intervals of one minute as the ball gradually cooled.

The method of reducing the observations was explained at length. The difference of the Napierian logarithms of the differences of temperatures of the junctions, indicated by the deflections, divided by the intervals of time, gives the rate of cooling; and this, multiplied by a factor depending on the capacity for heat of the ball and on the extent of its surface, gives the quantity of heat emitted in gramme water units in the unit of time per square centimetre, per 1° of difference of temperatures. Formule were given which express the results of the experiments very closely, and a table calculated by them exhibits the rates of emission for every 5o of difference throughout the range.

The first and second series had a range of from 5° to 25° only, which was too small to give decided results; but the third and fourth series, made with a polished copper surface and a blackened surface respectively, gave variations in the emissive power from 000178 at 50 diff. of temperature to 000226 at 60° diff. for the polished surface, and from 000252 at 5° diff. to 000328 at 60° diff. for the blackened surface; and the emissive powers of the two surfaces exhibit throughout a nearly constant ratio to each other of about 694.

On a Respirator for Use in Extinction of Fires.
By WILLIAM LADD, F.R.A.S.

This instrument combines the advantages of the charcoal and the cotton-wool respirators. The respirator is intended to be fitted on the heads of firemen, and it will enable a fireman to enter into the midst of any smoke, however dense. There is sufficient protection for the eyes, by means of glasses. The results of an experiment with the respirator have been stated by Prof. Tyndall. In a small cellar-like chamber, furnaces containing resinous pine-wood were placed, and the wood being lighted, a dense smoke was generated. In this room, Prof. Tyndall and his assistant, using these respirators, remained for more than half an hour, when the smoke was so dense and pungent that a single inhalation through the unprotected mouth and nostrils would have been perfectly unendurable. The instrument has been tested by Capt. Shaw, chief officer of the Metropolitan Fire Brigade, who has taken very great interest in perfecting it, by attaching to it suitable hoods.

On the Temperature-equilibrium of an Enclosure in which there is a Body in Visible Motion. By Prof. BALFOUR STEWART, F.R.S.

It is now several years since Professor Tait and the author of this paper came jointly to entertain the belief that there is some transmutation of energy, the exact nature of which is unknown, when large bodies approach or recede from one another. It is desirable to vindicate an idea of this nature, both from the theoretical and the practical point of view-that is to say, we ought, if possible, to exhibit it as a probable deduction from those laws of nature with which we are already acquainted; and, on the other hand, it ought to be supported by observations and experiments of a new kind. In our case the experiments and observations have been of a difficult nature, and are yet in progress; it is therefore premature to bring them before the notice of the Association. A theoretical vindication of the idea has been obtained by Professor Tait, and more recently one has occurred to the author of these remarks, which he now ventures to bring forward. Men of science are now sufficiently well acquainted with Prevost's theory of exchanges, and its recent extension. We know that in an enclosure, the walls of which are kept at a constant temperature, every substance will ultimately attain the very same temperature as these walls, and we know also that this temperature-equilibrium can only be brought about by the absorption of every particle being exactly equal to its radiation, an equality which must separately hold for every individual kind of heat which the enclosure radiates. This theoretical conclusion is supported by numerous experiments, and one of its most important applications has been the analysis of the heavenly bodies by means of the spectroscope. Let us now suppose that in such an enclosure we have a body in visible motion, its temperature, however, being precisely the same as that of the walls of the enclosure. Had the body been at rest, we know from the theory of exchanges that there would have been a perfect equilibrium of temperature between the enclosure and the body; but there is reason to believe that this state of temperature-equilibrium is broken by the motion of the body. For we know both from theory and experiment that if a body, such for instance as a star, be either rapidly approaching the eye of an observer or receding from it, the rays from the body which strike the eye will no longer be precisely the same as would have struck it had the body been at the same temperature and at rest-just as the whistle of a railway engine rapidly approaching an observer will have to him a different note from that which it would have had if the engine had been at rest. The body at motion in the enclosure is not therefore giving the enclosure those precise rays which it would have given it had it been at the same temperature and at rest; on the other hand, the rays which are leaving the enclosure are unaltered. The enclosure is therefore receiving one set of rays and giving out another, the consequence of which will be a want of temperature-equilibrium in the enclosure, in other words, all the various particles of the enclosure will not be of the same temperature. Now, what is the consequence of this? The consequence will be that we can use these particles of different temperature so as to transmute part of their heat into the energy of visible motion, just as we do in a steam-engine; and if it is allowable to suppose that during this process the moving body has retained all its energy of motion, the result will be an increase of the amount of visible energy within the enclosure, all the particles of which were originally of the same temperature. But Sir W. Thomson has shown us that this is impossible; in other words, we cannot imagine an increase of the visible energy of such an enclosure unless we acknowledge the possibility of a perpetual motion. It is not, therefore, allowable to suppose that in such an enclosure the moving body continues to retain all its energy of motion, and consequently such a body will have its energy of motion gradually stopped. Evidently in this argument the use of the enclosure has been to enable us to deduce our proof from the known laws of heat and energy, and we may alter the shape of the body without affecting the result; in other words, we should expect some loss of visible energy in the case of cosmical bodies approaching or receding from one another.

On a new Steam-gauge. By Prof. CH. V. ZENGER.

This gauge is intended to avoid the defects of common air-gauges, which have

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.
By THOMAS BLOXAM, Lecturer on Chemistry, Cheltenham College.

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