468 THE POPULAR SCIENCE MONTHLY. 



arguments may be adduced in favor of either view, although neither 

 can be yet demonstrated. 



The idea that a very few true elements, uniting together in a vari- 

 ety of proportions, may give rise to all the bodies which we now look 

 upon as elementary, derives perhaps its strongest support from an 

 analogy pointed out by Prof. Cooke something like twenty years ago. 

 He first called attention to the many serial relations which connect 

 the members of any elementary group, and then showed how much 

 these groups resemble the homologous series of organic chemistry. In 

 such a series we have a number of compounds each diflering from its 

 immediate predecessor in a very definite way. Thus, in the series of 

 alcohol radicles, we have first the hydrocarbon methyl. Adding to 

 this an atom of carbon and two of hydrogen, we get the second mem- 

 ber of the series ; the third is formed by the same addition to the 

 second, the fourth similarly derived from the third, and so on. The 

 difterence between the molecular weights of any two successive mem- 

 bers in this series is always the same. Just so in some groups of ele- 

 ments, as we have already seen. The atomic weight of lithium is 

 seven, add sixteen and we get that of sodium, while another increase 

 of sixteen gives the value of potassium. Again, the atomic weight of 

 sulphur is that of oxygen plus sixteen ; three times sixteen more brings 

 us to selenium, and another forty-eight reaches the equivalent of tel- 

 lurium. Here certain multiples of sixteen are missing ; do they cor- 

 resj^ond to the atomic weights of undiscovered elements ? Such a 

 speculation is curious, but not very profitable. 



The analogy, then, between the groups of elements and the homol- 

 ogous series of organic compounds is quite striking, although it may 

 not be very precise. Hence Cooke suggested that, if the elements 

 were compounds, their resemblances might be explained by supposing 

 them to form series like the hydrocarbons, yi which bodies of similar 

 constitution are akin in general properties. Now, this conception was 

 certainly very brilliant, and rendered intelligible many important facts 

 which before it were unclassified. It did not, however, suggest the 

 possible unity of matter, but merely put the ultimate question regard- 

 ing the nature of the elements a step farther back. Instead of many, 

 it gave us the idea of few elementary bodies ; why and how these 

 diflered were yet to be found out. Prof. Cooke was, fortunately, too 

 cautious a chemist to put forwaid views of this sort dogmatically ; 

 he did not offer a theory even ; he only made suggestions to be taken 

 later at their true value, whatever that might be. 



The other side of the question, that of the unity of matter, has 

 been worked up by several chemists in a variety of ways. Some have 

 studied the plienomena of crystallization and drawn their conclusions 

 therefrom ; others have taken up the subject from a dynamical point 

 of view. Given atoms of one kind only, how to arrange these in dif- 

 ferent aggregations so as to present all the phenomena offered by our 



