Dr. E. J. Mills on the Atomic Theory. 113 



defenders are not agreed. Dalton, for example (New System, 

 pp. 135, 136), conceives water to have an internal constitution 

 resembling square piles of shot arranged in successive horizontal 

 strata. " A vessel full of any pure elastic fluid " also " presents 

 to the imagination a picture like one full of small shot " (pp. 147 

 & 189). When two gases are mixed, an intestine motion ensues, 

 and continues " till the particles arrive at the opposite surface of 

 the vessel against any point of which they can rest with stability, 

 and the equilibrium at length is acquired when each gas is uni- 

 formly diffused through the other" (p. 190). Solids likewise 

 consist of arranged particles (p. 209). Hence it is evident that 

 Dalton regarded atoms as enjoying a perfect repose, unless when 

 mechanically or chemically disturbed. In this purely statical 

 contemplation he has been followed by most chemists, some of 

 whom have believed themselves to dissent wholly from his theory. 

 What is the theory of types, but an emanation from the prime 

 idea involved in the celebrated figures at the end of the * New 

 System ' ? The wooden models with which Dalton illustrated his 

 lectures have reappeared as glyptic formula?; and the material 

 existence of their connecting wires is perpetuated in fhe lines or 

 " bonds " of graphic formulas. 



But atoms have been considered from another point of view. 

 It has been found by not a few thinkers that rest is a condition 

 which falsely represents the facts of nature, and that atoms must 

 therefore be conceived as moving with an industry to which cessa- 

 tion is unknown. On this view, the state of dissolved salts and 

 the process of precipitation are explained much as Berthollct ex- 

 plained them, only in corpuscular language. Supposing, for 

 example, hydric chloride be added to aqueous cupric sulphate. 

 That cupric chloride is formed is shown by the green coloration 

 that ensues. Hence there has been a partition of the copper. This 

 is accounted for by supposing all the atoms in the mixture to 

 move constantly — by adopting, in short, the theory of greatest 

 effort. Another chemist observes that if all the atoms were per- 

 fectly free to move, no compound could be stable, and conse- 

 quently brings forward an hypothesis of "limited atomic mobility. n 



Considerations derived from chemical formula? have frequently 

 been adduced in favour of the atomic theory, and therefore de- 

 serve attention. The formula? themselves were at first the results 

 of experimental facts in quantitative analysis, and are therefore 

 independent of theory. Dalton first applied a method of sym- 

 bolic ratios, in which attention was especially drawn, first, to a 

 standard unit for each element, and secondly to that unit's co- 

 efficient. The standard unit is then taken as the atom ; a ne- 

 cessary consequence of which supposition is, that all coefficients 

 must be integral. It will be observed, however, that we are now 



Phil. Mag. S. 4. Vol. 42. No. 278. Aug. 1871. I 



