602 HISTORY OF SCIENCE. 



of phenomena. Very wide is the range of phenomena which the 

 atomic hypothesis embraced ; but whenever another hypothesis shall 

 be found covering with equal or greater consistency a still wider 

 range of phenomena, then the atomic hypothesis will be superseded. 

 The atoms are not objective facts ; they have never presented them- 

 selves to the senses. In Dalton's, and in all conceptions of the kind 

 it may be seen that the mental process consists in transferring to the 

 supposed existences those very properties which are observed in visible 

 and tangible masses of matter. Thus in the passages from Dalton 

 alluded to above, we have shape, solidity, atmospheres, densities, elasti- 

 city. It has been said that though with our present means of obser- 

 vation the objective existence of atoms is incapable of direct demon- 

 stration, yet it is not impossible but that by some immense extension 

 of the power of our microscopes we might be able to behold the atoms. 

 If this should come to pass, there would inevitably arise the very 

 same questions as to the constitution of the atoms that we now ask 

 ourselves about the constitution of matter. We should begin to spe- 

 culate about the still invisible atoms of which the visible atom might 

 be supposed to be constructed, and on which its properties would be 

 supposed to depend. The process could never terminate. Atoms 

 might be conceived within atoms : 



So naturalists observe a flea 

 Has smaller fleas that on him prey, 

 And these have smaller still to bite 'em, 

 And so proceed ad infinfaim. 



It has been laid down as necessary for a good theory that the laws 

 by which the theoretical agency is supposed to act must be the same, 

 or at least not greatly different from those according to which some 

 agency analogous to the supposed one is known to act ; or, on the other 

 hand, that we must refer the phenomena to an agent known to be con- 

 ceined in the action, and limit the theory to laying down hypothetical 

 laws as to the agent's mode of action. That is, we are not at liberty to 

 assume a wholly hypothetical agency acting according to laws inferred 

 only from the phenomena to be explained. Now, in adapting the atomic 

 hypothesis to the facts which new discoveries have from time to time 

 brought to light, chemists have been obliged to attach other hypo- 

 theses to the original one. The original hypothesis in its simplicity 

 has been found incapable of explaining the new classes of facts, and 

 therefore for each of these classes an extra hypothesis has been added 

 on to the original foundation, so that the theoretical structure of che- 

 mistry has somewhat of the aspect of an inverted pyramid, of which 

 Dalton's hypothesis is the apex. 



The theory of the existence of matter in particles of definite weight 

 perhaps now derives its validity less from the simple laws of chemical 

 combinations as propounded by Dalton than from its accordance with 



