PROGRESS IN NINETEENTH CENTURY 233 



particles, corpuscles or electrons, have been split off from ordinary 

 matter, and they are always the same, regardless of the element from 

 which they separate. Even their mass can be estimated, and it ap- 

 pears to be about the thousandth part of that which represents an 

 atom of hydrogen. These conclusions are perhaps not final, but they 

 are emphasized by the results obtained in the study of radioactivity. 

 The investigations of Rutherford and Soddy, of Ramsay, Dewar, 

 and others, all tend in the same direction, and lead to the suspicion 

 that the atoms are complex and subject to decay. The three most 

 radioactive elements are radium, thorium, and uranium, and these 

 have the highest atomic weights of any substances known. If the 

 elements are complex, these are the most so, and therefore presum- 

 ably the least stable. If we take this testimony in connection with 

 that given by Thomson, the evidence offered by the spectra of the 

 heavenly bodies, and the regularities of the periodic law, we have 

 a strong argument in favor of the supposition that the so-called ele- 

 ments are not the simplest forms of matter, and that they may be 

 ultimately one. The doctrines of unity of matter and the unity of 

 force are thus philosophically allied, and only negative evidence can 

 be adduced to support a belief in the actual diversity of the elements. 



Speaking broadly, organic and inorganic chemistry, at least as 

 they are commonly studied, are essentially descriptive in their 

 character, and they deal with statical phenomena. Physical chemis- 

 try, on the other hand, is more concerned with dynamics, and seeks 

 to determine the conditions of chemical equilibrium, and the nature 

 of chemical change. What substances are and what substances do 

 are of course only two phases of the same fundamental problem, 

 which are separable ideally, but not otherwise. Descriptive chemistry 

 lays stress upon one side of the science, physical chemistry emphasizes 

 the other; but they blend together by imperceptible degrees, and no 

 clear line of demarcation can be drawn between them. 



Every science, when viewed historically, is seen to have a central 

 line of growth, to which its various branches are naturally related. 

 In chemistry this line is marked by physical phenomena, and from 

 their study the greater generalizations have been derived. Avogadro's 

 law, the law of Dulong and Petit, Faraday's theory of electrolysis, 

 and the periodic classification of the elements are good illustrations of 

 this principle. The atomic theory itself, which connects all of the 

 other relations, is fully as much physical as chemical; valence is best 

 explained in electrical terms, and stereochemistry arose from optical 

 and crystallographic considerations. Physical chemistry is the main 

 stem of our science, and statical conditions are merely the results 

 of dynamical equilibrium. The description of a product is incom- 

 plete unless we have noted the physical phenomena, the trans- 

 formations of energy, which took place during its formation, and to 



