INTRA-ATOMIC ENERGY. 275 



day when Rontgeu, exainhiing' more closely the Crookes tubes which 

 physicists had been using- for more than twenty years without seeing 

 anj'thing- new in them, discovered that they gave out peculiar rays, 

 absolutely different from any then known, to which he gave the name 

 of X-rays, By this discovery a quite unforeseen thing, entirely new, 

 since it found no analogy of any kind in known phenomena, was placed 

 before the world of science. 



The discovery of the radio-activity of uranium followed closely upon 

 that of the X-rays, and had the consequences which 1 have already 

 stated. It led especiallv to the admission that the atoms of certain 

 bodies, supposed at first to be exceptional in character, possess the 

 extraordinary property of dissociating themselves, but, as I showed 

 that this property l)elongs to all bodies, it was necessarv to recognize 

 that there exists in matter a special and universal propert}' totally 

 unknown hitherto, and from which it results that the structure of 

 the atom is necessarily ver}^ different from that which had for a long 

 time been supposed. 



Premnt ideas as to the structure of atoms. — The first origin of our 

 present ideas concerning the structure of atoms was a consequence of 

 Faraday's discoveries in electroh^sis. He proved that the molecules 

 of compound bodies carr}" a charge of neutral electricity, definite and 

 constant in amount, which becomes dissociated into positive ions and 

 negative ions when solutions of metallic salts are traversed })y an 

 electric current. The atom was soon considered as composed of two 

 elements, a material particle and an electric charge which was believed 

 to be combined with it or sui)erposed upon it. 



In this phase of the evolution of ideas the positive electron and the 

 negative electron are merel}' two substances to bo added to the list of 

 elementary bodies with which the}- are capable of combining. The 

 idea of the material atom still persists. 



In the present evolution there is a tendency to go much further. 

 After asking themselves whether this material support of the electron 

 was realh' necessar}^ man}' physicists have reached the conclusion that 

 it is not. They reject it entirelv and consider the atom as wholly con- 

 stituted of an aggregate of electrical corpuscles without any material 

 suppoi't. The structure of matter would then be exclusively electrical. 



This is evidently a considerable step, and by no means all plu^si- 

 cists have yet taken it. Classical ideas pi-epossess our minds too 

 completely to be easily got rid of; but. judging from the general ten- 

 dency at the present time, it would seem quite possible that this idea 

 may itself l)ecome classical in its turn. 



As soon as the mat(MMal atom is generally considered as a simple 

 aggregation of (dectrie corpuscdes we are very (puckly led to admit 

 that it is only a condensjition of (MUM'gy. 



