AUTHOR'S PREFACE 



THIS EDITION 



The first edition of this book appeared in 1877, at the time of the 

 most rapid and beautiful development of the kinetic theory of gases. 

 About twenty years before, the founders of the theory, Kronig 

 and Clausius, had explained the expansive tendency of gases, 

 and had calculated their pressure on the assumption that the 

 smallest particles of gases do not repel each other, but are in rapid 

 motion. From the theory based on this supposition not only were 

 the laws of gases, so far as they were then known, deduced in 

 simplest fashion, but also new laws, hitherto undreamt of, were 

 discovered, which were afterwards confirmed when tested by 

 experiment. These results, which we owe to Maxwell and 

 Clausius, quickly won to the theory many friends and adherents. 



But a deeper insight into the new theory was not then widely 

 possessed, since the mathematical shape of the memoirs formed a 

 grave obstacle for many readers. I undertook therefore to exhibit 

 the kinetic theory of gases in such a way as to be more easily 

 intelligible to wider circles, and especially to chemists and other 

 natural philosophers to whom mathematics are not congenial. 

 To this end I endeavoured, much more than was otherwise usual, 

 not only to develop the theory by calculation, but rather to support 

 it by observation and found it on experiment. I therefore collected 

 together, as completely as I could, and summarised, the observa- 

 tions by which the admissibility of the theory might be tested and 

 its correctness proved. I dare to think that I have not failed in this 

 endeavour ; for not only did my book receive favourable judgment, 

 but also my presentation of the subject was turned to much 

 account in popular writings and found its way into physical text- 

 books. 



In this my book fulfilled the purpose I intended. I wrote it 

 only for that time, and did not seriously think that it might 



