affinity, cohesion referred themselves; it was the bond which bound together all other views. In this lies the extraordinary service which this theory rendered to science-viz., that it supplied a fertile soil for further advancement; a soil which was previously wanting. In the most recent investigations concerning the constitution of organic bases, the alcohols and the acids corresponding to the alcohols, we have seen that the groundwork of the Daltonian theory is equally valid for organic bodies. His main law, that the properties of compounds are dependent on the nature of their elements, and on the mode and way of their position or arrangement, will always maintain a high value.

Professor Roscoe, as President of the Chemical Section of the "British Association for the Advancement of Science" in 1870, after alluding to the views of Sir B. C. Brodie and Dr Odling, with which he mainly agreed, and believing that we must carefully distinguish between fact and theory, went on to say:

I would remind you that Dalton's discovery of multiple and reciprocal proportions (I use Dr Odling's word), as well as the differences which we now acknowledge in the power of hydrogen-replacement in hydrochloric acid, water, ammonia, and marsh-gas, are facts, whilst the explanation upon the assumption of atoms is, as far as chemistry has yet advanced, a theory. If, however, the existence of atoms cannot be proved by chemical phenomena, we must remember that the assumption of the atomic theory explains chemical facts as the undulatory theory gives a clear view of the phenomena of light; thus, for instance, one of the most important facts and relations of modern chemistry which it appears difficult, if not impossible, to explain without the assumption of atoms, is that of Isomerism. How otherwise than by a different arrangement of the single constituent particles are we to account for several distinct substances in which the proportions of carbon, hydrogen, and

Roscoe, Cannizzaro, and Tyndall.

299

oxygen are the same? Why, for instance, should 48 parts by weight of carbon, 10 of hydrogen, and 16 of oxygen, united together, be capable of existing as three different chemical substances, unless we presuppose a different statical arrangement of the parts by which these differences in the deportment of the whole are rendered possible?

Professor Cannizzaro of Palermo, now of Rome, delivered the "Faraday Lecture" to the Chemical Society, May 30, 1872. Nature of June 20 gives inter alia the following as part of the professor's lecture :

Whilst giving a broad sketch of the progress of modern chemistry, he showed that the atomic theory had become more and more intimately interlaced with the fabric of chemistry, so that it is no longer possible to separate them without rending the tissue, as it were, of the science, and that up to the present time we have been unable to enunciate even the empirical laws of chemical proportion independently of that theory; for those who employ the term equivalent, in the sense that Wollaston did, commit an anachronism. Consequently, in the exposition of the value and use of symbols, formulæ, and chemical equations, not only are we unable to do without the atomic and molecular theory, but it is inconvenient to follow the long and fatiguing path of induction which leads up to it. By one of those bold flights of the human mind we can at once reach the height whence we discern at a glance the relations between facts.

Professor Tyndall, who seconded a vote of thanks to Cannizzaro for his lecture, said :

The chemist cannot halt at equivalent proportions-he must ask himself whence they arise, and the inevitable answer is some form of the atomic theory. This theory, however, cannot be confined to chemical phenomena. The motions of those atoms and molecules underlie all our explanations of the physical cause of light and heat, and it is already taking up the

field of magnetism and electricity. Consider, for example, the heat of gases, both as regards the motion of translation of the molecules which produce temperature, and the motions of rotation and vibration of their constituent atoms, which, though they do not express themselves as temperature, constitute a portion of the heat.

Dumas, the most distinguished of French chemists. ("Leçons sur la Philosophie Chimique,” p. 221), calls Dalton "the Nestor of Chemistry;" and Wurtz ("Histoire des Doctrines Chimiques," Discour preliminaire, p. xiv.), after describing the relation between combining weights observed by Wengel and Richter, adds:

Mais l'interpretation théorique faisait encore defaut. Elle découle des travaux d'un savant anglais qui a doté la science de la concéption à la fois la plus profonde et la plus féconde parmi toutes celles qui ont surgi depuis Lavoisier. Au commencement de ce siècle, la chimie etait professée à Manchester par un homme qui joignait à un amour ardent de la science cette noble fierté du savant qui sait prèférer l'independance aux honneurs, et à une vaine popularité la gloire des travaux solides. Ce professeur est Dalton; son nom est un des plus grands de la chimie.

APPENDIX.

JOHN DALTON'S STATEMENT OF THE CASE IN THE AFFAIR BETWIXT HIS BROTHER AND SELF.

Article 1st. That my father, in apportioning the paternal inheritance to us, has made a vastly great and unusual distinction betwixt my brother and self.

Article 2d. That he would have placed his children upon a more equitable footing, if he had apprehended it was in his power to do so, with reputation to himself.

Article 3d. That it was in his power to dispose of the whole of his property according as he should think best; but from a great deficiency in the knowledge of the law, and from a want of advice suited to the exigencies of his situation at the time he made his will, he has not availed himself of his power.

Article 4th. That upon these considerations, I think myself entitled to something more out of the paternal inheritance than I have yet received.

I shall now state the facts, to the best of my knowledge, in support of these articles.

Facts relating to article 1st.-My father's property, when his verbal will was made, was a real estate, & of it freehold, the rest copyhold, let to farm for £41, 10s. p. ann. without the dwelling-house, now let for £2 p. ann. Total, £43, 10s. p. ann.

one of his children more than for another, except this be an instance.

Now, I appeal to any one who is acquainted with human nature, whether these facts, together with those that are related to have taken place at the time of the settlement, are better accounted for on the one supposition or the other; on the supposition that he knew very well he could cut off the entail at pleasure without meriting any just censure—or on the supposition that it was not in his power to do so, nor his business to meddle with it.

Facts relating to article 3d.-Every one who is acquainted with the laws of landed property in this country, knows that an entail may be defeated by the tenant in possession. Nothing more is required than to fee a few persons in office, who will, after a sham process, sufficiently guarantee the tenant against the effects of the iniquitous statute. This need not be further insisted upon. With respect to my father's knowledge about these quirks of law, we differ very much: my brother seems to think my father knew as much as the exigencies of his affairs required, and I think quite contrary. It is proper we advance what we have in support of our opinions. I believe father never read a printed page on law in his life. He seems to have had no idea of the difference of an estate tail and an estate for life, and the whole of his transactions and opinions seem to have been formed on the supposition of the estate being his for life only; I have no doubt that my grandfather designed Uncle Jona to have the estate for life only, and that father, if he survived, should have it fee-simple; however, father, when in possession, finding he had it not fee-simple, concluded the next descent would make it such, and told my brother so, who told it to me not many years ago. Now it is evident that he must have had a very imperfect idea of the tenure of an estate tail, to suppose that simple descent made any difference in the tenure of it. He was equally out of it in the persuasion that neither Aunt Mary D. nor my mother had any claim of dower, as E. and J. Robinson very well know.

I believe he refused J. Sandilands the farm of the stone quarries, from an idea that he had no right to let it. All these things prove him to have been greatly deficient in the knowledge