232 



SCIENCE. 



[N. S. Vol. XXII. No. 556. 



Even if I had the knowledge requisite 

 for a complete exposition of these investi- 

 gations, the limits of time would compel 

 me to confine myself to those parts of the 

 subject which bear on the constitution and 

 origin of the elements. * 



It has been shown, then, that the atom, 

 previously supposed to be indivisible, 

 really consists of a large number of com- 

 ponent parts. By various convergent lines 

 of experiment it has been proved that the 

 simplest of all atoms — namely, that of 

 hydrogen — consists of about 800 separate 

 parts ; while the number of parts in the 

 atom of the denser metals must be counted 

 by tens of thousands. These separate 

 parts of the atom have been called cor- 

 puscles or electrons, and may be described 

 as particles of negative electricity. It is 

 paradoxical, yet true, that the physicist 

 knows more about these ultra-atomic cor- 

 puscles and can more easily count them 

 than is the case with the atoms of which 

 they form the parts. 



The corpuscles, being negatively electri- 

 fied, repel one another just as the hairs on 

 a person's head mutually repel one another 

 when combed with a vulcanite comb. The 

 mechanism is as yet obscure whereby the 

 mutual repulsion of the negative corpuscles 

 is restrained from breaking up the atom, 

 but a positive electrical charge, or some- 

 thing equivalent thereto, must exist in the 

 atom, so as to prevent disruption. The 

 existence in the atom of this community 

 of negative corpuscles is certain, and we 

 know further that they are moving with 

 speeds which may in some cases be com- 

 parable to the volocity of light, namely, 

 200,000 miles a second. But the mechan- 

 ism whereby they are held together in a 

 group is hypothetical. 



It is only just a year ago that Thomson 

 suggested, as representing the atom, a me- 

 chanical or electrical model whose prop- 



erties could be accurately examined by 

 mathematical methods. He would be the 

 first to admit that his model is at most 

 merely a crude representation of actuality, 

 yet he has been able to show that such an 

 atom must possess mechanical and electric- 

 al properties which simulate, with what 

 AA^hetham describes as 'almost Satanic ex- 

 actness,' some of the most obscure and yet 

 most fundamental properties of the chem- 

 ical elements. 'Se non e vero, e ben 

 trovato, ' and we are surely justified in be- 

 lieving that we have the clue which the 

 alchemists sought in vain. 



Thomson's atom consists of a globe 

 charged with positive electricity, inside 

 which there are some thousand or thou- 

 sands of corpuscles of negative electricity, 

 revolving in regular orbits with great 

 velocities. Since two electrical charges 

 repel one another if they are of the same 

 kind, and attract one another if they are 

 of opposite kinds, the corpuscles mutually 

 repel one another, but all are attracted by 

 the globe containing them. The forces 

 called into play by these electrical inter- 

 actions are clearly very complicated, and 

 you will not be surprised to learn that 

 Thomson found himself compelled to limit 

 his detailed examination of the model atom 

 to one containing about seventy corpuscles. 

 It is indeed a triumph of mathematical 

 power to have determined the mechanical 

 conditions of such a miniature planetary 

 system as I have described. 



It appears that there are definite ar- 

 rangements of the orbits in which the cor- 

 puscles must revolve, if they are to be per- 

 sistent or stable in their motions. For the 

 purpose of general discussion, which is all 

 that I shall attempt, you may take it that 

 the number of corpuscles in such a com- 

 munity is fixed; and we may state that 

 definite numbers of corpuscles are capable 



