424 



SCIENTIFIC THOUGHT. 



planet between Mars and Jupiter, anticipating the dis- 

 covery of the Asteroids, which have accordingly been 

 regarded as the fragments of the missing planet. 

 27. It thus appears that purely " chemical reasoning," as it 



between has been called, has proved insufficient to establish the 



chemical 



and physical atomic view of nature on the same firm basis as has 



reasoning. 



supported the mechanical or astronomical view ever since 

 the age of Galileo and Newton. 1 In the second half of 

 the century, the atomic view of matter has however 

 been put forward from a different side, and independent 

 researches have, in combination with the older chemical 

 theories, introduced so much definiteness into this line 

 of thought that " the Newtonian theory of gravitation is 



1 ' ' Many diagrams and models 

 of compound molecules have been 

 constructed. These are the re- 

 cords of the efforts of chemists to 

 imagine configurations of material 

 systems by the geometrical rela- 

 tions of which chemical phenomena 

 may be illustrated or explained. 

 No chemist, however, professes to 

 see in these diagrams anything 

 more than symbolic representations 

 of the various degrees of closeness 

 with which the different com- 

 ponents of the molecule are bound 

 together. In astronomy, on the 

 other hand, the configurations and 

 motions of the heavenly bodies are 

 on such a scale that we can ascer- 

 tain them by direct observation ; 

 . . . the doctrine of universal gravi- 

 tation not only explains the ob- 

 served motions of our system, but 

 enables us to calculate the motions 

 of the system in which the astro- 

 nomical elements may have any 

 values whatever" (Clerk Maxwell, 

 ' ' On the Dynamical Evidence 

 of the Molecular Constitution of 

 Bodies," June 1875, 'Scientific 

 Papers,' vol. ii. p. 418). "The 



chemists ascertain by experiment 

 the ratios of the masses of the 

 different substances in a compound. 

 From these they deduce the chemi- 

 cal equivalents of the different sub- 

 stances, that of a particular sub- 

 stance being taken as unity. The 

 only evidence made use of is that 

 furnished by chemical combination. 

 It is also assumed, in order to ac- 

 count for the facts of combination, 

 that the reason why substances 

 combine in definite ratios is, that 

 the molecules of the substances 

 are in the ratio of their chemical 

 equivalents, and that what we call 

 combination is an action which 

 takes place by a union of a mole- 

 cule of one substance to a molecule 

 of the other. This kind of reason- 

 ing, when presented in a proper 

 form, and sustained by proper evi- 

 dence, has a high degree of cogency. 

 But it is purely chemical reasoning ; 

 it is not dynamical reasoning. It 

 is founded on chemical experience, 

 not on the laws of motion" (Id. 

 article " Atom," ' Ency. Brit.,' 1875 ; 

 ibid., vol. ii. p. 456). 



