600 HISTORY OF SCIENCE. 



We might as well attempt to introduce a new planet into the solar 

 system, or to annihilate one already in existence, as to create or destroy 

 a particle of hydrogen. All the changes we can produce consist in 

 separating particles that are in a state of cohesion or combination, and 

 joining those that were previously at a distance. 



" In all chemical investigations it has justly been considered an 

 important object to ascertain the relative weights of the simples which 

 constitute a compound. But unfortunately the inquiry has terminated 

 here ; whereas, from the relative weights in the mass, the relative 

 weights of the ultimate particles or atoms of the bodies might have 

 been inferred, from which their number and weight in various com- 

 pounds would appear, in order to assist and guide future investigators 

 and to correct their results. Now, it is one great object of this work 

 to shew the importance and advantage of ascertaining the relative weights 

 of the ultimate particles both of simple and compound bodies, the number 

 of simple elementary particles which constitute the compound particles, 

 and the number of less compound particles which enter into the formation 

 of one more compound particle. 



" If there be two bodies, A and B, which are disposed to combine, the 

 following is the order in which the combination may take place, begin- 

 ning with the most simple, namely : 



" i atom of A + i atom of B = atom of c, binary. 



1 atom of A + 2 atoms of B = atom of D, ternary. 



2 atoms of A + i atom of B = atom of E, ternary. 



i atom of A + 3 atoms of B = atom of F, quaternary. 



3 atoms of A + i atom of B = atom of G, quaternary, etc. , etc. " 



In the course of the work the experiments are detailed which give 

 support to these views. The author gives plates in which the ultimate 

 atoms of the chemical elements are represented by arbitrary signs, 

 consisting of circles distinguished by some mark or letter. The an- 

 nexed examples will serve as specimens of Dalton's graphic represen- 

 tations of the ultimate particles. 



It will be observed that Dalton speaks of c, D, E, F, and G as 

 atoms. This is of course a departure from the original meaning of the 

 word, which denotes something incapable of any division, whereas 

 these binary, ternary, etc., atoms are divided when the compounds 

 are resolved into their elements. No little confusion has at times 

 arisen from this ambiguous use of the term atom. " Ultimate particle 

 of water" would be a better expression for Q Q than " atom ;" " ulti- 

 mate," because by further division it would cease to be water, and, 

 become an oxygen atom Q an< ^ a hydrogen atom Q . 



The definiteness of theoretical view which Dalton's hypothesis gave 

 to chemistry has proved of wonderful service to the science. It be- 

 came the bond by which chemical theory is linked to that of other 



