philosopher, whatever idea be entertained on the subject of their import and of their future, have had at any rate this result, that they have led chemists to take into account certain laws of symmetry in arranging the formulæ of compound bodies. The corrections based on them, proposed by M. Gaudin forty years ago, have been confirmed by experiment; they have paved the way for the rearrangement of the formulæ of all compounds of carbon or of silicon-that is to say, of all compounds of organic origin, and of almost all those the investigation of which constitutes mineralogy properly so called.

The absolute defence of dualism retained no partisans after the last struggles which Berzelius maintained with singular brilliancy towards the end of his life in the interest of this doctrine.

It is to be observed that the electrochemical theory, regarding the elements of bodies as obeying the two electrical forces, and the materials of every compound as uniting in twos to form by successive agglomerations, and always two by two, gradually more complicated combinations, proceeded in harmony with the French nomenclature. It is not, therefore, surprising that the use of the molecular system proposed by Ampère, modified by M. Gaudin, and generally adopted with divers variations by the chemists who, being occupied with organic chemistry, are obliged to take account of the phenomena of substitution, has both rendered less ardent the pursuit of a precise electrochemical theory, and less confident the too absolute interpretation of the French nomenclature.

We are thus led to conclude that, on the one hand, the search for an electrical theory of affinity now occupies but few-although beautiful and useful applications of electro-chemistry have been accomplished of late years, and are pursued with great success; on the other hand, that it is no longer possible to represent by means of the dualistic nomenclature the multitudinous chemical compounds which the molecular system registers daily.

We are thus more and more led towards the experimental investigation of chemical types as a basis of the classification of compounds, apart from any hypothesis on the internal arrangement of their elements,-which constitutes the true foundation of the French nomenclature properly understood.

At the same time we are led towards the idea which attributes to the molecules of compound bodies a more complex constitution than would be derived from the binary nomenclature, and which makes of them planetary or crystallographical systems. presenting several centres of force-mobile in the first case, fixed in the second.

We finally revert to the thought which would directly connect affinity with universal attraction.

In recent times the views of Newton have met with an unexpected and remarkable support in the beautiful and important researches which our eminent colleague M. Henri St.-Claire Deville has devoted to the phenomenon of dissociation-one of the greatest acquisitions, not only of chemistry, but of natural philosophy.

Nothing, in fact, is more in accordance with the laws of mechanics than to say that a volatile liquid placed in connexion with a free space fills it with its vapour, and that the tension of this increases or decreases regularly in a continuous manner according as the temperature rises or falls.

But to say that carbonic acid separates from lime in the same manner, to establish that there is a tension of decomposition analogous to the tension of vapours, and that the evaporation of a liquid and the decomposition of a carbonate take place in virtue of the same laws, and present the same phenomenon of continuity, is to connect chemical combination with cohesion, is to prove that under certain conditions the laws which regulate the aggregation or the separation of molecules of the same kind are also applicable in the case of molecules of different kinds.

Without affirming that in all cases the dissociation of compounds presents the character of a continuous phenomenon, it is enough that the case is frequent (as is proved by the researches of our eminent compeer and those of his pupils), to justify our assimilating the purely physical molecular separations and the chemical molecular separations, and to give us the right henceforth to unite cohesion and affinity the one to the other, and both to universal attraction.

It follows from this brief summary :—

(1) That Newton gave of chemical affinity a notion to which nothing has been added, when he connected it with general attraction and showed how, at a certain distance from the centres of molecular action, it may become zero, or even repulsive.

(2) That Ampère has given the complement to this view by showing that the shape of the components limits the number of combinations which two elements may produce, and that it determines the ratios according to which they may unite, and even enables us to predict the ready replacement of one element in a complex molecule by another without its stability being compromised.

(3) That Meyer has shown how the impact of molecules, striking against each other with extreme velocity to produce combination, may give rise to the phenomena of heat, of light, and of electricity which accompany chemical action.

(4) That M. Henri St.-Claire Deville, in discovering the capital phenomenon of dissociation, has opened a new way to science

by closely connecting chemical combinations with the purely physical phenomenon of the formation of vapour.

(5) Finally, that the doctrines with the aid of which it has been attempted to explain chemical phenomena by a distinct unknown cause, or by electricity, have yielded no fruit; while those which tend to bring it under the laws of universal attraction consolidate themselves, approach more and more to the facts, and indicate better and better the path of progress.

It would then be natural, just, and useful that Newton's name, and the definitions he gives, both of molecular attraction and of chemical atoms, should be retained in works intended for instruction in chemistry. In my opinion (but I give it with all the reserve which such subjects demand), heat is the real measure of chemical energy, while light and electricity may for the present be regarded by the chemist either as agents of which he makes use, or as phenomena whose appearance he ascertains.

Matter and heat would still be, as in Lavoisier's time, the definition of the two objects to which the thoughts of chemists should especially be directed.

The time will doubtless come when, the laws which molecular attraction obeys being themselves known, we shall be able to predict or explain the formation of compounds, their destruction, the preferences and the choice of elements in the formation of combinations, the special affections which acids or bases exhibit in the production of salts; but before attacking this last and difficult problem, we must know otherwise than by suppositions the bond which connects the shape of the crystals of one chemical species with the arrangement of the atoms the grouping of which constitutes the molecules which are the materials of these crystals.

I hope the Academy will pardon my having so long occupied it with these historical considerations, and that it will understand the interests attached to them.

My object would be attained if, on the one hand, I had contributed still more vividly to direct the attention of chemists to the relations which connect the motions of heat with the transformations of matter, and if, on the other, I had shown that the principle of the French nomenclature is not unsuited to the classing and naming the compounds of organic or molecular chemistry.

Lavoisier, in proposing the new nomenclature, stated that the Commission, of which he was the eloquent organ, "had been unwilling to devote itself to great discussions on the constituent principles of bodies and on their elementary molecules that it had severed itself from the systematizing chemists, who are always ready to accompany facts by an apparatus of reasoning in which

the fact itself disappears, and in whose hands science becomes an edifice raised by their imagination."

He declared, finally, that the Commission "had sought to apply to chemistry the logic which belongs to all sciences-the name of class or genus recalling, in the natural order of ideas, properties common to a great number of individuals, and that of species properties peculiar to certain individuals."

I do not know whether I am deceiving myself; but it seems to me, moreover, that this duel of antagonist molecules which is met with in all the phenomena of chemistry, and which the present nomenclature expresses so well, remains incontestable, and that we should not give up depicting it until we are forced to do

But the act of combination once accomplished, the duel terminated, the French nomenclature does not pretend to say that the two bodies which have acted on each other have retained their distinctive character in the molecule formed and are not confounded in a complex system. It is in this respect that Berzelius, going beyond Lavoisier's idea, exaggerated the meaning.

It is not without a legitimate satisfaction that we have the right to say in this circle, that, notwithstanding the progress which has metamorphosed the field of chemistry, the Academy has nothing to regret, either as regards doctrine or language, of what our illustrious predecessors had founded with so much prudence, wisdom, and even genius.

XIII. On the Heating of a Disk by rapid rotation in vacuo. To the Editors of the Philosophical Magazine and Journal. GENTLEMEN,

WITH

7ITH reference to the paper of Herr O. E. Meyer, which you translated in the last Number of the Philosophical Magazine, we desire to make the following remarks.

There was no assumption (Annahme) whatever in our statement of the small but unavoidable deviation of the axis from perpendicularity to the disk. The amount of this bias was, in each case, directly measured by turning the disk so slowly that no flexure could possibly be produced by the rotation; and the amount thus determined was not visibly exceeded even at the highest speeds. The length of the axis is nearly 4-5 inches (or more than twothirds of the radius of the disk); and it lies in two bearings which fit it as tightly as is consistent with free rotation. The utmost amount of deflection of the edge of the disk due to slackness of these bearings cannot possibly be nearly as great as 0·001 inch. Herr O. E. Meyer supposes, contrary to the usual principles of ordinary dynamics, that a change of position of the instantaPhil. Mag. S. 4. Vol. 37. No. 247. Feb. 1869. H

neous axis of the disk necessarily implies loss of vis viva, and he calculates the supposed loss in very peculiar manner. What he means by saying that vis viva lost by impact of the axle on its bearings is employed in heating the disk (alle übrige lebendige Kraft geht für die Rotation verloren und wird zur Erwärmung der Scheibe verwandt) we cannot pretend to understand. Such a statement, if meant to be understood literally, would appear to be contrary to the fundamental principles of thermodynamics. If, however, though he certainly does not say so, Herr Meyer means that impact of the axle on the bearings may produce vibrations of the disk which in time will by viscosity be frittered down into heat, he merely repeats one of many objections, long ago perceived by ourselves, and also pointed out to us by others, an objection which we have already at least partially met by experiment and calculation. [It may be well to say here that Professor Helmholtz, nearly two years ago, very kindly detailed to us his objections, making several valuable suggestions by which we have since endeavoured to profit, and which will be duly acknowledged when we are in a position completely to answer these objections. This will, we hope, soon be the case, as extensive additional apparatus is now in course of construction.]

There are various other parts of Herr Meyer's paper to which we might easily take exception, especially the calculation he makes (even supposing his assumptions to be correct) as to the absolute amount of radiation to be expected; but it would be foreign to our present object to enter into such details. The determination of radiation in absolute measure is an inquiry of great importance, and we are glad to hear that it has been taken up by Professor Neumann; we believe that Sir W. Thomson also has been working at it; so that the question is now in good hands, and will no doubt soon be definitely answered. We are, Gentlemen,

January 1869.

Yours &c.,

B. STEWART,
P. G. TAIT.

IN

XIV. Fundamental Principles of Molecular Physics.

By Professor W. A. NORTON*.

N a recent work by Joseph Bayma, S. J., Professor of Philosophy, Stonyhurst College, England, in which a new theory of Molecular Mechanics is ably set forth, I find a brief critique of my theory of Molecular Physics, published originally in Silliman's Journal, and republished in the London and Edinburgh * From Silliman's American Journal for September 1868.