Mention has already been made of the “New View of Dalton’s Atomic Theory,” which Roscoe published in collaboration with Dr. Harden. This book is of considerable interest and value in regard to the genesis of a conception which marks a turning-point in the history of chemistry. From a careful study of Dalton’s manuscripts and note-books which had been discovered in the rooms of the Literary and Philosophical Society of Manchester, the authors were led to conclusions concerning the origin of the atomic theory of chemistry which differ fundamentally from those which had been generally accepted. It had hitherto been supposed that it was the experimental discovery of the law of combination in multiple proportions which, in his search for an explanation of this fact, led Dalton to the idea that chemical combination consists in the approximation of atoms of definite and characteristic weight, the theory of atoms being adopted to explain the facts discovered by chemical analysis. In reality the exact opposite was the case. It was the theory of the existence of atoms of different weights that led Dalton to the discovery of the facts of combination in multiple proportions. The late Dr. Debus, some two years previously in a pamphlet published at Cassell, had reached a similar conclusion from a study of Dalton’s published works, but by a different line of argument. As a matter of priority there is no doubt that to Debus belongs the credit of first pointing out that the commonly accepted view of the genesis of Dalton’s atomic theory is erroneous, but it is no less true that the method of reasoning by which he came to that conclusion cannot be substantiated even if it is not actually disproved by the evidence from Dalton’s note-books. Of course the idea of atoms, that is, of small indivisible particles, did not, as is popularly supposed, originate with Dalton: it is older than Science itself. How and where it first arose cannot be exactly stated. Dr. Debus attributes it to Moschus, a Phœnician philosopher living at Sidon about 1100 B.C. It was resuscitated by Gassendi in the middle of the seventeenth century, and applied by Boyle, who speaks of it as the Phœnician philosophy, to the explanation of chemical phenomena. Newton made use of it to explain Boyle’s law and the “spring of air.” Dalton almost certainly derived it from Newton, with whose corpuscular notions he was quite familiar, and employed it to explain the phenomena of diffusion and absorption. He was therefore quite ready to extend it to all gaseous phenomena, and indeed to chemical phenomena in general, to the extent that it seemed applicable.