ON THE EVOLUTION OF THE ELEMENTS. 127 



bring forth fruit abundantly. I need only say I would like to see the 

 whole subject reconsidered, now that it is clear that an isolated body in 

 space need not of necessity get cooler, although continually losing heat. 



There is a small question of nomenclature, the retention of the word 

 atom, now that atoms have been shown to be changeable, which may appear 

 justified if we consider the history of the word. The Greek meaning con- 

 veyed by the word was purely an imaginative one, being, in fact, the 

 smallest particle of matter that can be imagined. From the time of 

 Dalton a new experimental meaning became attached to the word, to 

 signify the smallest part of an element, or the unit, that enters into 

 chemical change, and since chemical changes were the most fundamental 

 then known, the word signified in a derived sense the smallest particle 

 that can exist. To-day the atom still retains the exact meaning it has 

 had for a century, as the unit of chemical change, but chemical change is 

 not now the most fundamental known. Radioactive change is so utterly 

 different that it cannot be considered to have any relation to chemical 

 change. 



The view has been expressed to me that since the radio-elements have 

 been shown to undergo changes, it is incorrect any longer to speak of their 

 atoms, and the word molecules would meet the case. But this would 

 cause the word atom to drop out of scientific use altogether, for no 

 element is safe from the fate which has been shown to overtake the radio- 

 elements. On the other hand, if we used the word violecule throughout 

 where now we use atom, and spoke of a molecule of hydrogen where now 

 we mean atom, we should have to revive the old clumsy nomenclature of 

 simple molecules meaning atoms, and compound molecules meaning mole- 

 cules. 



Limitation of Present Methods. — Our knowledge of material evolution 

 has arisen almost entirely on account of the energy emitted in the pro- 

 cesses, the material evidence, as in the proof of the production of helium 

 from radium, being of necessity only confined to a few cases. The general 

 condition which determines whether any process of spontaneous evolution 

 comes within our experimental methods of detection is simply that the 

 energy evolved should be sufficient in quantity and suitable in kind. 

 There is no doubt that in the actual case of the radioactive elements the 

 conditions are exceptionally favourable. Probably in no other bi-anch of 

 physics can such a minute evolution of energy be detected and accurately 

 measured as in radioactivity. The electroscope is the oldest and simplest 

 as it is the most sensitive electrical instrument, and in proper hands pos- 

 sesses possibilities for accurate measurement by no means to be despised. 

 It may seem to conflict with what has been said as to the enormous quan- 

 tities of energy liberated during radioactive processes that such delicate 

 methods should be demanded, but that is because the actual amount of 

 matter changing is always infinitesimal, even under the most favourable 

 circumstances. The world is old, and only those changes which require 

 an aeon for completion continue still. 



Since the theory of atomic disintegration w.as advanced it has become 

 more and more plain that such disintegration may, and does, occur with- 

 out the accompaniment of radioactivity. We now rather regard radio- 

 activity as a gratuitous hint given us, one might almost say overlooked, 

 by nature into secrets we were not bound ever to have known of at all. 

 For the same result and the same type of evolution could have been 

 accomplished, and may actually be going on, without our possessing any 



