Other departments of physics were not neglected. For instance, one of his greatest investigations was that on the kinetic theory of gases. Geniuses had been working before him on this line, for, as pointed out by Professor Tait, this theory owed its origin to Daniel Bernoulli, the greatest mathematician of the eighteenth century, and had been developed by the successful labors of Herapath, Joule and, above all, of Clausius. The work of these men put the general accuracy of the theory beyond all doubt and led to its very general acceptance, yet the details of it needed to be elaborated before it could become definitely scientific. Its greatest developments are due to Maxwell, and in this field Maxwell appeared as an experimenter on the laws of gaseous friction as well as a mathematician. His work with regard to color had showed his ingenuity as an experimentalist, and this is still further illustrated by his carefully arranged experiments on gases. Indeed, his work in this line makes it very clear that nothing was too difficult for him, and that anything that he turned his hand to in the field of science he was sure to accomplish with eminent success. It was not only his scientific monographs, however, that indicate how great a scientist Clerk Maxwell was, but his text-books, even those of more or less elementary character, which he wrote bring out this same idea. He wrote, for instance, an admirable text-book on the theory of heat, which went through many editions. Students of the subject, even those who were not far advanced, found it clear and easier of study than many a less exhaustive work. He also wrote an elementary treatise on matter and motion, which has gone through several editions. One might think that so small a work would scarcely interest him enough to tempt him to put forth his powers at their best, and that at most it would be a conventional condensation of previous knowledge. Prof. Tait, who surely must be taken as a good judge in the matter, says that "even this, like his other and larger works, is full of valuable material worthy of the most attentive perusal not of students alone, but of the very foremost scientific men."