-114 TRANSACTIONS OF THE 
haps under our very eyes but at such slow rates, and’so 
quietly that it has escaped observation. 
Since radioactive disintegration, so far as observed, 
always proceeds by the elimination of electrons or of 
-helium atoms, it would seem to be suggested that these 
two are constituents of all matter. Such is perhaps the 
case for the electron, as any substance, apparently can 
be made to give off electrons, and the electrons from all 
substances are apparently identical. The helium ‘atom, 
however, cannot be the only primitive element, and for 
two reasons. In the first place we know one element of 
“atomic weight less than that of helium, and in the second 
place the atomic weights of all the elements are not 
multiples of 4. A discussion of the hypothetical’ consti- 
tution of the atom:is perhaps not in the province of a chem- 
ist, and would be beyond the limit of this paper. It has 
-been suggested, however, and with a large degree of rea- 
-gonableness, that the atoms of all chemical elements ‘are 
made-up of combinations of atoms of two, or: perhaps 
three elements. 
W. D. Harkins has brought forward such ‘a system 
in which he uses hydrogen ‘and helium as the two primi- 
tive elements, while Nicholson uses hydrogen ‘and two 
hypothetical elements, nebulium, of atomic weight 1.6281, 
and’ proto-fluorine, of atomic weight 2.8615. It is to be 
noted that the sum of the atomic weights of these two 
-hypothetical elements is almost exactly the atomic weight 
of helium. 
CONCLUSION AND RESUMBP’. 
The older conception of the chemical atom was 
characterized by its simplicity. The atoms of any’ given 
elements were all alike, were homogeneous and indivis- 
able. ‘The physical and chemical properties’ of the atom 
were a function of the mass of the atom, its atomic weight. 
The present conception of the atom, which needléss 
‘to say isstill changing in its details, regards the atom as a 
‘complex’ system, composed of various units. These-units 
“are, (1), atoms of hydrogen, or helium, or of both, ‘or 
‘perhaps atoms of substances as yet’ unknown, ‘and €2), 
vel@ctrons. The mass of the atom is principally rep- 
resented by the first. 
