418 



SCIENTIFIC THOUGHT. 



as to fixed and multiple proportions, expressed himself 

 with great reserve as to the value of the atomic hypothesis, 

 and when drawing up a table of atomic weights, he pre- 

 ferred to call them equivalents a term used already by 

 Cavendish as implying no other meaning than that they 

 fix the proportions in which bodies combine into, or sep- 

 arate out of, compounds. Davy was hesitating and re- 

 luctant to admit any hypothesis as to the ultimate con- 

 stitution of matter. Liebig l and Faraday, 2 at a somewhat 



1 " In endeavouring to develop 

 the theory which at present pre- 

 vails respecting the cause of the 

 unchangeableness of chemical pro- 

 portions, let it not be forgotten 

 that its truth or falsehood has 

 nothing whatever to do with the 

 natural law itself. The latter is 

 the expression of universal experi- 

 ence ; it remains true, invariably 

 and immutably, however our no- 

 tions respecting its cause may from 

 time to time vary and change." 

 Thus wrote Liebig (' Familiar Let- 

 ters on Chemistry,' 1844) at a time 

 when great confusion existed as to 

 the real atomic or smallest com- 

 bining weights which should be 

 assigned to the chemical elements ; 

 when in consequence many chemists 

 preferred to discard the word 

 "atomic weight" altogether, and to 

 revert to the term equivalent (see 

 Kopp, ' Entwickelung der Chemie,' 

 p. 718, &c.) Dumas in 1840 de- 

 clared that the term atomic weight 

 did not deserve the confidence with 

 which chemists made use of it : if 

 he could he would banish the word 

 atom from chemistry, convinced as 

 he was .that science should not 

 transgress the limit of that which 

 could be known by experience. 

 Liebig, in 1839, about the time 

 when his important memoirs on the 

 constitution of organic bases and 

 acids appeared in his ' Annals,' em- 



phasised likewise the fact that 

 equivalents never change ; but he 

 doubted whether chemists would 

 ever agree as to the relative atomic 

 weights, and he hoped the time was 

 not far distant when they would 

 all return again to equivalents 

 (ibid., p. 438). In France an in- 

 fluential school, headed by the 

 eminent M. Berthelot, up to the 

 present day limits itself to the use 

 of equivalents. See Berthelot, ' La 

 Synthese chimique,' 7 me e"d., p. 

 164 n. 



2 The objections which Faraday 

 urged against the notion of atom 

 and atomic weight seem to come 

 from a different quarter. In 1834, 

 when explaining his researches on 

 electro - chemical action, he says 

 ('Exper. Res.,' No. 869): "If we 

 adopt the atomic theory or phrase- 

 ology, then the atoms of bodies 

 which are equivalents to each other 

 in their ordinary chemical action 

 have equal quantities of electricity 

 naturally associated with them. 

 But I must confess I am jealous of 

 the term atom; for though it is 

 very easy to talk of atoms, it is 

 very difficult to form a clear idea 

 of their nature, especially when 

 compound bodies are under consid- 

 eration." Ten years later, in his 

 'Speculation touching Conduction 

 and the Nature of Matter' (see 

 'Exper. Res.,' vol. ii. p. 285), 



