1915^ Recent Conceptions of the Atom 119 



element has proved very difficult and one definition after an- 

 other has been given up as knowledge has grown. 



The atomic theory must stand until a better theory is form- 

 ulated explaining the laws of combination. This theory in its 

 simple form is independent of speculation as to the nature of the 

 atom. Of course the views as to this nature have greatly changed 

 with the growth of knowledge and the chemist has learned to be 

 cautious in his attempts at definition. It is enough for him to 

 know that the supposedly unchanging atom is at least unchanged 

 by the forces and the conditions with which he works and that 

 he can safely count upon it to act in the future as it has in the 

 past. It cannot be decomposed so far as is known by any means 

 at his command and even if such decomposition were effected the 

 laws of combination would remain the same. 



It may not be simple or a unit in itself. In fact, both 

 chemist and physicist have long known multiplied reasons for 

 believing in its complexity, but under the influences of forces 

 that bring about combination and decomposition it behaves as a 

 simple unit. And so, while the study of this complexity is most 

 fascinating, the discovery of the nature and constitution of the 

 atom can make no change in the part it has played in the up- 

 building of chemical science. 



But this science is deeply concerned with the constitution of 

 matter. It is the prime object of its striving and we can no 

 longer look upon the atom as the ultimate particle. The num- 

 erous light waves of different length revealed in the spectra, the 

 intimate relationship sho'wn in the periodic system, and other 

 facts forbid this. We must go deeper, if possible, and find out 

 how the atom itself is built up. 



Prout, in 1814, thought of the atom as built up of hydrogen. 

 Graham in 1863, conceived of one ultimate, common atom in 

 different conditions of movement. In 1887, Crookes suggested 

 a hypothetical primal atom, protyle, which, under the influence 

 of electricity, gave rise to the various elemental atoms. These 

 were, of course, speculations without basis of experiment and 

 serve mainly to show the trend of thought. In fact, being be- 



