290 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 13 



some, at least, of the elements were really unstable. The evolution of 

 helium from radium, discovered by Ramsay and vSoddy, made the 

 evidence for this instability complete ; a derivation of one element from 

 another had actually been observed. 



These discoveries opened a new field of research; and it was soon 

 found that the elements at the top of the atomic weight scale, namely, 

 uranium and thorium, are spontaneously but slowly decaying, yield- 

 ing more than thirty new substances which differ widely in point of 

 stability. To each one a half -life period is assigned, measured in 

 some cases by thousands of years, in others by fractions of a second. 

 Among these are two new varieties of lead ; one derived from uranium, 

 the other from thorium, which chemically are not distinguishable 

 from ordinary or normal lead except by differences in their atomic 

 weights and their specific gravities. The lead from thorium has an 

 atomic weight about a unit higher, and that from uranium about a 

 unit lower, than the atomic weight of normal lead. To this class of facts I 

 shall refer later, as evidence in support of my arguments. That 

 chemical elements can decay is the essential fact to be remembered. 



That the chemical elements were formed by a process of evolution 

 from the simplest forms of matter can hardly be doubted now, but the 

 process is not yet ended. They were developed at high temperatures; 

 but when a certain stage was reached in the cooling mass they began 

 to combine with one another to form the new class of substances which 

 are known as compounds. These, obviously, represent an advanced 

 degree of complexity, with corresponding instability; and with vary- 

 ing conditions both combinations and decompositions, such as are 

 reproducible by human agencies, constantly occur. By this extension 

 of the evolutionary process the solid Earth was built up, but in princi- 

 ple the process is the same throughout. From the formation of the 

 first elements to the chemical changes now taking place upon the 

 Earth there is no real interruption. One line of progress has been 

 followed until a maximum of natural complexity and instability is 

 reached in the organic compounds which form the basis of all physical 

 life, whether vegetable or animal. The same fundamental matter, 

 governed by the same fundamental laws, appears from beginning to 

 end of the evolutionary process. 



Between the formation of an element and the formation of a com- 

 pound there is, however, an apparent difference. The first stage of 

 the process was one which required a vast period of time, the second 

 stage is marked by rapidity. The series of elements was slowly 



