August 9, 1877] 



NATURE 



293 



disjoined. Thus it is that, even during the history of an 

 individual intelligence, "practice makes perfect," by fre- 

 quently repeating the needful stimulations along the same 

 lines of cerebral discharge — so rendering the latter even 

 more and more permeable by use. Thus it is that a 

 child learns its lessons by frequently repeating them ; 

 and thus it is that all our knowledge is accumulated. In 

 a word, if, as has been truly said, "man is a bundle of 

 habits," we have in Mr. Spencer's theory of nervo-genesis 

 a physical explanation of the fact. And forasmuch as it 

 is upon this theory that Mr. Spencer may be said to 

 found that great monument of modern thought — his 

 " Principles of Psychology," I cannot but feel that 

 one of the most important bearings which my work 

 on the Medusas has had, is that of supplying facts 

 which tend to substantiate this theory — and this at a 

 time when it seemed as though the theory could never 

 have other than a priori considerations for its sup- 

 port. But if my interpretation of these facts is correct, 

 this important theory is now receiving inductive verifica- 

 tion from a most unexpected source. At first sight no 

 two organic structures could well seem to have less in 

 common than the swimming-bell of a Medusa and the 

 brain of a Man ; nor could anything seem more unlikely 

 than that a great psychological theory should derive sup- 

 port from the study of polypes, where the very existence 

 of a nervous system has only just been discovered. But 

 here again, I believe, we may discern the uniformity of 

 Nature ; and while watching the passage of the waves 

 of stimulation in the contractile strips of Aiinlia—novi 

 passing freely, now stopped by an excess of resistance, 

 and now again forcing a passage, — I have felt that I 

 was probably witnessing, on the lowest plain of nervo- 

 genesis, that very same play and counter-play of forces, 

 which, on the highest plain of nervo-genesis, invariably 

 accompanies, if it does not actually cause, the most in- 

 ti'icate reasoning of a Newton, the most sublime emotion 

 of a Shakespeare, the most imperious will of a Napoleon, 

 and the most transforming thought of a Darwin.' 



ATOMS AND EQUIVALENTS 



IN the Comptes Rcndiis for the month of May and June 

 there is a series of communications by Messrs. Wurtz 

 and Betthelot containing a discussion of their respective 

 views as to whether chemical changes should be expressed 

 by elements in equivalent proportions or whether the 

 more modern system of atomic weights should be 

 employed. 



In the first communication, which is made by M. Wurtz, 

 he remarks on the discrepancy evidently existing between 

 his idea and that of M. Deville, " who has criticised him 

 in a former number of the journal," on the law of volumes 

 of Gay-Lussac. He advances in support of the atomic 

 argument, that free hydrogen may be regarded as a com- 

 bination of two atoms of hydrogen, the peculiar reaction 

 of hydrochloric acid on hydride of copper and in the 

 case of oxygen with oxygen the reactions discovered by 

 Thenard and Brodie of peroxide of hydrogen on certain 

 oxides. He maintains that the molecular conceptions 

 with regard to bodies in the free state are further upheld, 

 in the case of nitrogen by the formation of nitro and 



* Throughout the lecture of which the above is a pretty full abstract, 1 

 have associated Mr. Herbert Spencer's theory of nervo-genesis with his 

 name excUisively. To avoid misapprehension, therefore, \ append this 

 note to state that I am not ignor.tnt of the fact that the theory in question 

 has occurred to other thinkers as well as to the great English philosopher. 

 Moreover, I am quite aware that even if this theory of nervo-genesis had 

 never been enunciated a priori by any speculative thinker, some such theory 

 would certainly have been devised ii posteriori hy any working physiologist 

 of moderate capacity who might first happen to observe such facts as are 

 above detailed. But considering that Mr, Spencer elaborated the theorj- 

 deductively, and that he did so in a much more thorough and painstaking 

 manner than had ever been done before, considering, too, that he has given 

 the theory so elaborated such a prominent place in his system of objective 

 psychology, I have not hesitated to describe this theory as being pre-emi- 

 nently a product of hii authorship. — G. J. R. 



dinitro compounds, and in the case of carbon by the con- 

 sideration of organic chemistry when examined according 

 to the theory of Kekule of the grouping of several carbon 

 atoms in the same molecule. After discussing the law of 

 Gay-Lussac as applied to the gaseous compounds of 

 hydrogen with chlorine, oxygen, and nitrogen, he remarks 

 that what results from the previous discussions on this 

 matter, is, that the system of expressing chemical reac- 

 tions by equivalents which prevailed about 1840 over the 

 atomic notation of Berzelius, has not taken into proper 

 account the discoveries of Gay-Lussac on the combination 

 of gases with each other ; and consequently, that the 

 maintenance of this principle in the discussion of chemical 

 phenomena would cause a serious obstacle to the 

 advancement of the science. 



M. Berthelot on behalf of those who, like himself, retain 

 the method of writing chemical changes by equivalents, 

 as opposed to the atoinic notation, in replying to this first 

 communication of M. Wurtz, states that he does not 

 think the matter to have the same importance which the 

 latter seems to attach to it. He considers that the 

 progress of chemical science is not entirely subordinate 

 to a change of notation which does not strike at the 

 foundation of the science as it had done a hundred years 

 ago to the pneumatic chemistry of Lavoisier. He thinks 

 that at the present day the truths are so general that all 

 the laws may be expressed to a certain extent by both 

 languages with equal clearness and precision. With 

 regard to the view put forward by Wurtz, that bodies in 

 the free state are composed of two atoms, and in support 

 of which view he has mentioned the reactions of 

 hydrochloric acid on hydride of copper, and peroxide of 

 hydrogen on oxide of silver, Cu.,H + HCl = CUCI2+ HH, 

 and Ag.,0 -\- H^O., = Ag, -f HJO + OO. M. Berthelot 

 deems the explanation given by M. Wurtz mere assump- 

 tion, without sufficient proof, tending to prevent a true 

 understanding of the real cause of the reaction. He also 

 considers that the true explanation might be found in and 

 explained by certain thermical considerations. 



M. Berthelot passes next to a criticism of the atomic 

 method of expressing the reactions of certain metallic 

 salts with each other, and complains of the doubling of 

 the equivalents of certain bodies, such as CaCl.,, which 

 he thinks makes an unnecessary complication in the 

 expression of the reactions, and gives as an instance the 

 reaction of certain nitrates with chlorides. By the system 

 of equivalents, he maintains they might be expressed by 

 one reaction— MNOe + M'Cl = MCH- M'NO^— but that 

 by the atomic notation four different and distinct reactions 

 are necessary to express their decomposition. 



M. Berthelot then alludes to the confusion he thinks 

 has arisen between the words law and hypothesis, in the 

 acceptance of Avogadro's law. In this case he maintains 

 that Avogadro and Ampere have enunciated, not a law, 

 but an hypothesis, in saying, " All gases contain the same 

 number of molecules in the same volume," having, in 

 reality, nothing by which to conceive the idea of a mole- 

 cule. On the other hand, he thinks the proposition, 

 "The densities of gases or vapours are proportional to 

 their equivalents," being deduced from two orders of 

 properties observable by experiment, may be regarded as 

 a true law. Partisans of the atomic notation have, he 

 considers, substituted for this the proposition, " Molecules 

 of simple gases contain the same number of atoms," and 

 he complains that they thus introduce two hypothetical 

 notions, that of the molecule, and that of the atom. On 

 the other hand, supporters of the system of equivalents 

 say, " Equivalent weights of simple or compound bodies 

 occupy the same volumes ;" or the volumes are to each 

 other in the simple ratios, 1,2, 3, 4, &c., thus : — 

 I equivalent of oxygen occupies i volume. 

 I „ CI, H, or Hg occupies 3 volumes 



I „ HCl occupies 4 volumes, &c. 



M. Wurtz, on the other hand, replaces the above by the 



