10 JOURNAL OF THE 
when these combining numbers, or atomic weights, were 
compared strange and interesting symmetries appeared. The 
times were not ripe for an explanation of their meaning, and 
such crude assumptions as that of Prout, that the elements 
were composed of hydrogen, or that of Low, that they were 
made up of carbon and hydrogen, were too baseless to com- 
mand much genuine support or to withstand much careful 
analysis. The important feature of agreement between such 
theories was the belief that the elements were composite and 
had one or more common constituents. 
From the comparison of one property, the atomic weights, 
the next step was to the comparison of all the properties. 
This comparison is brought out clearest and best for us in 
the Periodic System. Hereall the properties are very care- 
fully tabulated for us. The study of the system leads indis- 
putably to the conviction that this is not an arbitrary, but a 
natural arrangement, exceedingly simple in its groundwork, 
but embodying most fascinating symmetries, which hint of 
great underlying laws. He who looks upon it as a mere table 
of atomic weights has lost its meaning. It tells, with no un- 
certain note, of the kinship of the elements and ieads to a 
search after the secret of their interdependence and of their 
common factor or factors. There is so much which is made 
clearer if we assume a composite nature for the elements that 
many do not hesitate to make the assumption. 
Still another indirect method of approaching that problem 
is by analogy with bodies whose nature and composition are 
known. A very striking symmetry is observed between the 
hydrocarbons, and these in the form of compound radicals 
show a strong resemblance to certain of the elements. This 
analogy need not be dwelt upon here. It has been recog- 
nized for a long time and tables of hydrocarbons have been 
constructed after the manner of the Periodic System. Now 
these bodies are simply built up of carbon and hydrogen in 
varying proportions, and in any one homologous series the 
increments are regular. We know that they are composite 
and that they have but two common factors, carbon and hy- 
drogen. 
