'^'3'S THE CAXADIAX NATUEALIST. [^^ol- '^ii 



Dal ton fouDd, iu fact, that, in cases where two substances com- 

 bine in several proportions, if the quantity of one of them remains 

 constant, the quantities of the other vary according to very simple 

 relations. The discovery of this fact was the starting-point of 

 the atomic theory. Here is the substance of this theory : — That 

 which fills space, viz. matter, is not infinitely divisible, but is 

 composed of a universe of invisible, imperceptible particles, which., 

 nevertheless, possess a real extension and a definite weight.. 

 These are atoms. In their infiniteh attenuated dimensions, they 

 oflFer points of application to the physical and chemical forces. 

 They are not all like each other, and the diversity of matter is 

 owing to inherent differences in their nature. Perfectly identical 

 for the same simple body, they differ from one element to another 

 in their relative weights, and perhaps by their form. Affinity: 

 sets them in motion, and when two bodies combine with eacb 

 other, the atoms of the one are drawn towards the atoms of the; 

 other. As this approach always takes place in the same manner 

 between a determinate number of atoms, which are in juxtaposi- 

 tion one to one. or one to two, or one to three, or two to three — 

 in other words, according to very simple proportions, but invari- 

 able for a given combination — it results therefrom that the s?nallr- 

 est particles of this combination present a fixed composition! 

 rigorously similar to that of the entire mass. 



Thus the most important fact of chemistry, the immutability 

 of the proportions according to which bodies combine, appears 

 as a consequence of the fundamental hypothesis that chemical 

 combinations result from the coming together of atoms possessing 

 invariable weights. Berzelius compared these atoms to minute 

 njagnets. He imagined them to have two poles where the twoi 

 electric fluids are separated but unequally distributed, so that one 

 of them is in excess at one of the poles. '• There exist, " he said 

 •• atoms with excess of positive fluid and others with excess of 

 negative fluid" : the first attract the second, and this attraction, 

 the source of chemical affinity, preserves the atoms under all com- 

 binations. At the moment that these last are formed they are 

 set in motion ; in the completely formed compound they ai^ at 

 rest, and are divided as if into two camps, at once kept together 

 and maintained in opposition by the two electric fluids of oppo- 

 site kinds. 



Thus the electro-chemical theory, ingeniously adapted to the 

 liypothesjs of atoms, raised the dualism of Lavoisier to the dig- 



