456 Notices respecting New Books. 



yet, elements, but quasi- or meta-elements. Our notions of a chemical 

 element have been enlarged ; hitherto the elemental molecule has been 

 regarded as an aggregate of two or more atoms, and no account has been 

 taken of the manner in which these atoms have been agglomerated. The 

 structure of a chemical element is certainly more complicated than has 

 hitherto been supposed. We may reasonably suspect that between the 

 molecules which we are accustomed to deal with in chemical reactions, 

 and the component or ultimate atoms, there may intervene sub-molecules, 

 sub-aggregates of atoms, or meta-elements, differing from each other 

 according to the positions which they occupy in the very complex 

 structures commonly known as didymium, yttrium, and the like." 



A careful consideration of this important utterance by Mr. 

 Crookes will lead readers to the conclusion that, after all, the re- 

 solution of the rare earths by the methods of fractionation and 

 phosphorescent spectra may simply be a separation into modifica- 

 tion of the nature of isomerides or polymerides having different 

 optical properties. The basic element or metal may be the same 

 form of matter throughout whole groups, and if so we should 

 expect that compounds giving different " radiant " spectra would 

 give identical emission spectra under the influence of the more 

 violent disruptive discharge. The problem appears to require attack 

 from this side also before we can hope to arrive at any finality. 



The article on Mineral ogical Chemistry is short and is con- 

 tributed by Mr. L. Fletcher, of the British Museum; this is 

 sufficient guarantee of its soundness. About 7 pages are devoted 

 to an important discussion of the Molecular Constitution of Bodies 

 by Prof. J. J. Thomson. In the first part of this article the author 

 gives a brief account of the researches which have led to the con- 

 clusion that matter possesses a molecular structure, and he then 

 proceeds to consider the theories of such structure. Although 

 Prof. Thomson's article is essentially physical it is well in place in 

 the present volume; the points of contact between chemistry and 

 physics are in fact becoming more and more numerous with the 

 progress of research and speculation. To give one example : in 

 discussing Von Helmholtz's theory of the " electric charge on the 

 atom," the author says : — " On this view of molecular structure 

 the 'bonds of affinity' of chemists have a distinct physical mean- 

 ing, as they are the tubes of electrostatic force connecting the 

 atoms." It is impossible to do more than give this brief reference 

 to Prof. Thomson's article ; it must be read to be appreciated at its 

 full value, which in our judgment is certainly the highest among 

 the contributions to the volume. The article on Molecular Weights 

 by Mr. Muir is a kind of appendix to the article on Atomic and 

 Molecular Weights in the first volume necessitated by the later 

 researches of Baoult, and the application of this investigator's 

 methods to the determination of the molecular weights of chemical 

 compounds. 



Considerable space is devoted to Molybdenum and its compounds 

 by Mr. Muir ; and his co-editor, Dr. Morley, treats of Naphthalene 

 in a lengthy contribution of over 40 pages. This article is very 



