PROBABILITY AND ENTROPY 139 



number of objects would in general be a curve. 

 A straight line and an even chance are assumed 

 when there seems to be no "sufficient reason" 

 for a more complicated assumption. 



I cannot here describe in detail the theory of 

 probability and its many useful applications, 

 but must content myself with a brief discussion 

 of its application to one science which, because 

 it stands apart from all others, is of great philo- 

 sophical interest. The sciences of geometry, 

 statics, dynamics, electromagnetics, all assume 

 a knowledge in full detail of the system under 

 investigation. The science of thermodynamics, 

 on the other hand, ignores all detail. We are 

 given a box of unknown contents with two Tvdres 

 protruding, and are told that there is a certain 

 voltage between these two wires. We are also 

 told that when a certain current is drawn from 

 the wires a certain amount of heat is given off 

 bv the box. From these factors alone we calcu- 

 late what the voltage between the wires will be 

 when the temperature of the room changes. A 

 person who has known only the sciences of 

 detail that I have mentioned, and later realizes 

 the powerful support which he may obtain from 

 this science which knows no detail, is like a 

 swimmer who learns various strokes by which 



V) 



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