lo Bateman, TJie Physical Aspect of Time. 



deduced for the transverse mass of a moving electron* is 

 in fairly good agreement with the results of Kaufmann's 

 experiments, and has been verified very closely in a recent 

 experiment made by Bucherer. 



At present the theory is being widely used as a 

 working hypothesis, and is of great theoretical import- 

 ance, as it enables us to pass from the known analytical 

 specification of a phenomenon for a medium at rest to 

 the corresponding case of a medium in motion. It has 

 been used in this way by the late Hermann Minkowski to 

 obtain a scheme of electromagnetic relations for ponder- 

 able bodies in uniform motion, and has been shown by 

 Planck and \'on Mosengeil to provide a very useful 

 method of studying the properties of radiation in a cavity 

 in a moving body. 



With regard to the ideas of time that have arisen in 

 connection with the theory, it may be mentioned that two 

 new terms have been introduced. The term local time is 

 used by Lorentz to denote time as it is measured by a 

 set of observers who are moving uniformly in a straight 

 line relative to a standard set of observers. The relation 

 between the local time and the standard time is a reciprocal 

 one, the local time for one set of observers being the 

 standard time for the other set, and vice-versa. 



A second term, used by Minkowski, is Eigcnzeit or 

 the "proper time." It is defined for each particle and 

 may be regarded as the age of a particle. As a particle 

 moves from one point to another, the increase of age 

 depends upon the increase of the standard time, and also 

 upon the velocity of the particle. If the particle is moving 



*This formula is in— ° where ;;/ is the mass which the elec- 



y^ 



tron would have if it were at rest. 



