THE ATOMIC VIEW OF NATURE. 427 



method for determining the combining weights of elements 

 or their simple multiples, they did not draw the natural 

 consequences as to the physical constitution of bodies in 

 the gaseous state which followed from these and other 

 facts which had been known before. It had been known 

 since the time of Boyle and Mariotte that equal volumes of 

 different gases under equal pressure change their volumes 

 equally if the pressure is varied equally, and it was also 

 known through Gay-Lussac himself that equal volumes of 

 different gases under equal pressure change their volumes 

 equally with equal rise of temperature. The like be- 29. 



Avogadro's 



haviour of equal volumes of different gases towards pres- hypothesis, 

 sure, temperature, and chemical combination suggested 

 to Avogadro, and almost simultaneously to Ampere, the 

 very simple assumption that this is owing to the fact that 

 equal volumes of different gases contain an equal num- 

 ber of smallest independent particles of matter. This is 

 Avogadro's celebrated hypothesis. It was the first step in 

 the direct physical verification of the atomic view of mat- 

 ter, and if maintained by further experience, it was des- 

 tined to be one of the most important proofs of this view. 

 But this assumption or hypothesis had to be reconciled 

 with facts. It was, for instance, observed that a given 

 quantity of hydrochloric acid gas occupied the same 



showed the real meaning and im- ally the graphic description by L. 



portance of Avogadro's hypothesis. Meyer himself of the meeting held 



A good exposition of the difference in September 1860 at Carlsruhe 



of opinions which were held at that for the purpose of ventilating these 



time will be found in A. Wurtz, important theoretical questions (L. 



' La Theorie atomique,' p. 55, &c. Meyer's translation of Cannizzaro's 



See also Prof. Bedson's ' Memorial ' Sunto di un corso di filosofia 



Lecture' on Lothar Meyer (1896), chitnica,' in Ostwald's 'Classiker 

 in the 'Journal of the Chemical ; der exacten Wissenschaften,' No. 



Society,' p. 519, &c., and especi- 30, Appendix, p. 58). 



