first approximation, which must be perfected by a more profound study and a more perfect knowledge of the phænomena.

I have commenced the study of the physical properties of bodies with the velocity of sound, which is a function of several other properties which must correspond to it if the mathematical laws are correct, or which must modify those laws in whatever respect they are incorrect.

I determined the velocity of sound in solids by causing very fine and long wires to vibrate longitudinally; I diminished the diameters until the sound remained invariable. My wires were only from ths toths of a millimetre in diameter, and 1.50 metre in length. I placed them horizontally above a beam of oak, and fixed their extremities between two strong brass vices.

The wires were very homogeneous, and the harmonics exactly followed the laws of Bernoulli. The elevation of the sounds was given by a sonometer, of which the brass cord was very fine and very homogeneous.

The following formulæ give the velocity of sound as a function of the other physical elements ::

a, velocity of sound; g, force of gravity; E, coefficient of elasticity; A, mechanical equivalent of the heat, which I take as equal to 420 kilogrammetres; A, coefficient of linear dilatation; p, chemical equivalent; c= specific heat, and k=pc=38 to 42.

Except for zinc, the difference between the values of A, calculated and observed, are not very great, and must be attributed to causes of which the influence can be appreciated; in general the phænomena agree perfectly with the law.

Velocity of sound in gases and saturated and non-saturated vapours, for certain pressures and temperatures.

This portion of my researches was commenced some years ago with apparatus which I have been constantly bringing to perfection, and which I have rendered so simple and convenient that a chemist or physicist may take the velocity of a sound as easily as the density of a gas or vapour. The impossibility of employing sufficient time continuously in my experiments had always suspended my labours, until in M. Mérit, Professor at the Collége Rollin, I found an assistant of equal zeal and talent, with whom I have been able to resume and bring them to a good conclusion. Of the two means which I employ in taking the velocity of a sound in gases and vapours, I shall describe the more simple.

The apparatus consists of a glass balloon capable of containing 25 to 30 litres. Its neck, which is very short, is cemented into a brass ferule which bears three tubes, two horizontal and opposite, and one vertical or placed in the axis of the balloon. The latter bears at its lower part an organ-pipe placed in the centre of the balloon, and its exterior extremity receives a metal bellows, set in motion by a copper rod fixed normally upon the moveable bottom. One of the ho

rizontal tubes may be employed by means of a stopcock with three branches, to produce a vacuum in the apparatus and fill it with gas; to the other metal tube, which is also furnished with a safetystopcock, a curved glass tube dipping into the mercurial trough is adapted. By means of this arrangement the pressure of the gas may be ascertained, or it may be collected for analysis. With gases, the apparatus, with the exception of the bellows, is immersed in a trough full of water, and with vapours, the whole apparatus, including the bellows, is placed in a large zinc stove, where it is heated by the vapour of boiling water. For operating under low pressures, the bellows is surrounded by a box in which a counter pressure is established. This box and the rod of the bellows are then united by a caoutchouc tube, the elasticity of which leaves the rod sufficient play.

In a new apparatus with which I have not yet experimented, I have placed the bellows in the neck of the balloon, in order to avoid opposite pressures.

The apparatus being filled with gas or vapours, the sound is produced very pure, and as often as may be desired, by the action of the bellows; the harmonics issue readily, and it is necessary to take several in order to be certain of the fundamental sound.

show by the velocities of the sound the ratios k, and k of the specific heats of a gas and of the air; then the same specific heats at a constant volume c',, and at a constant pressure c1.

the values of this proportion derived from the rapidity of the sound, or from the specific heats at a constant pressure, are equal to the number of simple atoms which enter into the composite atom, or in a simple relation with this number.

Conclusions.

1. All gases resounding in the same pipe present the same nodal surfaces for the harmonics of the same order.

2. The formula by which Laplace expresses the velocity of sound is confirmed by experiment.

3. The law of Dulong and Carnot upon the specific heats of gases is conformable to the mechanical theory of heat and to experiment. 4. The velocity of sound in a gas is independent of the pressure and of the state of saturation: it depends entirely on the temperature. 5. The velocity of sound and direct experiment give the same values for the specific heats of gases at constant pressure.

6. With simple or composite gases, the specific heat at a constant volume is represented by the number of simple atoms of which they are composed, or by a simple fraction of this number.

7. For each simple or compound body there exists a ponderable molecule, the mass of which is always in simple proportion to the chemical equivalent, and which possesses the power of producing the same mechanical work when it is solicited by the same force or by the same quantity of heat. We shall give it the name of mechanical equivalent. The mass of this molecule will be that which must be taken as unity in problems of chemical dynamics.

THE IMPROVED INDUCTION COIL.

To the Editors of the Philosophical Magazine and Journal

GENTLEMEN,

I should not have replied to the Note from Mr. Bentley, contained in your last Number, but that I wish to prevent any misinterpretation of my remarks relative to Dr. Noad and himself. Mr. Bentley, in coming forward to vindicate the disinterested conduct of Dr. Noad, has quoted detached portions of my statements in such a connexion with each other as to endeavour to make it appear that I have complained of commercial injury sustained by Dr. Noad's having exhibited his machine, and asks, "Would it have been just to suppress my humble attempts at improvement for the sake of Mr. Hearder's pecuniary advantage?" Now I beg to say that this is quite a mistake. I have not complained of Dr. Noad's having introduced Mr. Bentley's machine to the public, because it was part of his business, as a public lecturer, to herald scientific improvements. I have only complained that Dr. Noad should have suppressed my inventions on that occasion, knowing that they had been made

upwards of twelve months before, and had been confided to him for publication more than six months previously, particularly when, on hearing that he was going to lecture, I reminded him of the position in which he had placed me, and requested that he would do me the justice to allude to my improvements at the same time. Why this request was denied to one to whom Dr. Noad had professed so much friendship, I cannot understand.

With regard to our respective claims to priority, I can only say that my machine was finished six months before the time when Mr. Bentley states that he commenced his; and I had also worked out most of the results contained in my communications to the Philosophical Magazine long before that period. It is a remarkable circumstance that there is no part in Mr. Bentley's arrangement which did not previously exist in mine.

I have the honour to remain, Gentlemen,
Your obedient Servant,

28 Buckwell Street, Plymouth,

June 13, 1857.

JONATHAN N. HEARDER.

ACTION OF NITRIC ACID UPON GLYCERINE.

Dr. Debus has succeeded in obtaining from glycerine and nitric acid, besides two or three other compounds, an acid belonging to the propyle series, and homologous to glyoxylic acid. The detail of this investigation will be published in a future Number of this Journal.

ANALYSES OF THE SULPHATO-CARBONATE OF BARYTES OF

THOMSON. BY DR. HEDDLE.

I believe it to be pretty generally understood among mineralogists, that the sulphato-carbonate of barytes of Thomson is merely the carbonate encrusted more or less with minute crystals of the sulphate: two analyses which I have lately made confirm this view. a. From Dufton; b. from Hexham (portions of crystals upwards of 4 inches in diameter).

538

INDEX TO VOL. XIII.