Literary Notices. 457 



Such are the defects of the simple refracting telescope; 

 which depending, as we have seen, upon optical laws, and 

 inherent in the construction, are irremediable, excepting by a 

 modification of the construction itself. Fortunately for the 

 interests of science, such a modification is possible, and has 

 been effected with admirable results : but the explanation of it 

 must be deferred to a future time. 



LITERARY NOTICES. 



Manual of the Metalloids, by James Apjohh, M.D., E.R.S., 

 M.R.I.A., Professor of Chemistry in the University of Dublin. 

 Longmans. — This work belongs to Galbraith and Houghton's series 

 of scientific annuals, and is intended as a " Hand-book in Chemistry 

 for Students in Medicine and Engineering." We should assign to 

 it a much wider range of utility, as it appears to us an admirable 

 introduction to chemistry, for students of all kinds. There is some 

 inconvenience in publishing a manual of the " metalloids" by them- 

 selves ; but we presume the chemistry of the metals, and of organized 

 bodies, will follow sufficiently soon to enable the subscribers to 

 Messrs. Gralbraith and Houghton's series on " Experimental and 

 Natural Science" to have a complete work on chemical science with- 

 out much delay. Any division of substances founded on their chemical 

 relations must necessarily partake of the incompleteness arising from 

 imperfect knowledge ; but as a provisional plan, little objection can be 

 made to the formation of two groups, metals and metalloids, provided 

 it is remembered that the division is purely empirical, and not in- 

 tended to embody any well-established theory. According to this 

 plan, opaque, highly lustrous bodies, which are good conductors of 

 electricity and heat, are called metals, while the elementary gases, 

 sulphur, selenium, tellurian, chlorine, bromine, fluorine, phos- 

 phorus, arsenic, boron, silicon, and carbon are lumped together under 

 the designation metalloids. 



Dr. Apjohn is too sound a thinker to be satisfied with this 

 arrangement; but there can be no doubt, that in the study of 

 chemistry the so-called metalloids should be presented to the learner 

 before the metals, and in the order in which they occur in his 

 book. The new manual consists of two portions — an introduction 

 of 105 pages devoted to the theoretical portion of chemistry, and 

 the main body of the treatise, in which the several metalloids and 

 their compounds with each other are briefly but compendiously 

 described. So far as the latter part is concerned, Dr. Apjohn 

 appears merely as an able compiler, and we do not notice any par- 

 ticular novelty in the treatment ; but the introduction constitutes a 

 work of great merit, in which his skill as a teacher is conspicuously 

 displayed. We doubt whether it would be possible to point to any 

 other book in which so many important facts and doctrines of 

 chemical philosophy are so briefly and so intelligibly explained. In 

 this section we find the laws of combination, equivalent numbers, 



