422 LIFE OF DALTON : 



weights, it is only the relative weight of the atoms of different 

 substances, which enters into the question. The term Atom 

 denotes the simplest and smallest combining proportion of 

 any body. Of their positive weight in relation to any known 

 quantities we are absolutely ignorant ; nor has any path been 

 disclosed through which such knowledge may hereafter be 

 reached. We can hardly say that the value of the discovery 

 is less from this abatement of its extent, since for all pur- 

 poses of science the relative weights are always the object 

 sought for, and carried into use. Again, these discoveries 

 teach nothing certain as to the figure or absolute magnitude 

 of such primitive atoms. Dalton, indeed, was led by various 

 considerations to regard them as spherical, and to delineate 

 them as such. But this, however probable, is still specula- 

 tive to our knowledge ; and certain isomorphic phenomena 

 might rather suggest several primitive forms than that of 

 the spherical atom alone. Such inference is especially justi- 

 fied as regards the combining atoms of compound bodies. 

 Here theory, rational in itself, somewhat outruns actual 

 knowledge ; but is continually and closely followed by it. 



As respects the question of magnitude, all that can be sought 

 for with any hope is the relative magnitude of these elemen- 

 tary parts. This enquiry, though far less simple and cer- 

 tain than that of relative weights, has been pursued with much 

 zeal and some success both by English and German chemists, 

 though under the form of comparison of atomic volumes 

 rather than atomic diameters. The distinction here involved, 

 and the general relation of volumes to other conditions of 

 matter under the atomic theory, would have demanded fur- 

 ther notice had the limits and design of this article made 

 it possible. We may briefly say, that the estimate by volumes, 

 though never willingly acquiesced in by Dalton himself, fully 

 confirms in every part the principles of the atomic theory ; 

 and as respects its particular application to the discovery of 



