SECOND LAW OF THERMODYNAMICS 233 



of which is infinitely manifold, and no completely adequate science can 

 ever be developed. 



Physical science, then, aside from those branches which are de- 

 pendent upon the atomic theory, consists of three branches, namely, 

 (1) mechanics, including hydraulics, electricity and magnetism, light 

 and sound; the science of those phenomena in which turbulence may 

 for practical purposes be ignored; (2) statistical physics, the science 

 of those phenomena in which turbulence introduces an appreciable and 

 practically important erratic element. Such phenomena can be studied 

 only by the statistical method, the record of individual cases and the 

 study of averages. Meteorology is the best example of statistical 

 physics, although every physical phenomenon has its statistical aspect; 

 and (3) thermodynamics. Some of the features of thermodynamics 

 have already been pointed out. It is the study of changes of state of 

 substances. A most important aspect of thermodynamics remains, 

 however, to be considered and the preliminary idea of this new aspect 

 may be obtained by drawing a parallel. In every-day life we see the 

 fire-insurance companies concerned with certain broad features of sta- 

 tistical physics in their examinations and records of fires, and we see 

 them also concerned with a profit and loss account which is wholly 

 abstracted from the details of the phenomena of conflagration. 

 Thermodynamics is the profit and loss branch of physics as it were; 

 and like the profit and loss branch of fire insurance, thermodynamics 

 is completely abstracted from any consideration of the details of any 

 physical phenomenon. Thermodynamics is concerned with the meas- 

 urement and counting of that type of physical degeneration which 

 accompanies turbulence just as fire insurance is concerned with the 

 estimate and counting of what we might call, using a fine phrase, 

 structural degeneration by fire. 



Thermodynamic Degeneeaton 



Every one has a feeling of the irretrievable effects of disaster, the 

 collapse of a bridge, the destruction of a house by fire, or the wreck 

 of a ship; these things involve losses which indeed may be forgotten 

 after reconstruction, but never balanced. The havoc wrought is essen- 

 tially irreparable. It is desirable to use the word degeneration in 

 a very narrow technical sense when we come to consider the second 

 law of thermodynamics, and the way may be paved to a clear under- 

 standing of the later and accepted use of this word in physics by 

 applying it now to designate that aspect of disaster which is irreparable. 

 The burning of a building, for example, is a process of degeneration. 

 It is very important, however, to avoid the carrying over of this idea 

 of structural degeneration into thermodynamics, where a much more 

 limited conception of degeneration arises. The term thermodynamic 



