130 PSYCHO-PHYSICAL METHOD 



figures assigned as the measure of the action-time by 

 Helmholtz and by Martius respectively. 



I have not time to show you how, having devised what 

 seems to be a satisfactory procedure, one may go on to 

 determine a number of interesting points. But I would 

 like to draw your attention to the fact that the results 

 of these psycho-physical experiments have an important 

 practical application. 



Such experiments may seem to you very remote from 

 any bearing upon practical life, and to the vulgar mind 

 they might seem for that reason to be useless. Now, if 

 they had no such bearing, that would be no reason for 

 pursuing such researches with any less ardour. For 

 all such results of experiment go to the building up of 

 psychophysical science ; they are essential elements of 

 the complete structure, though they may be neither 

 foundation-stones nor head-stones of the corners. 



Nevertheless, it is a legitimate source of satisfaction 

 a satisfaction of which no scientific worker need feel 

 ashamed when the results of researches, undertaken 

 from the point of view of pure science, are found to have 

 practical applications. 



It is, therefore, interesting to note that these psycho- 

 physical experiments have an important bearing upon 

 the work of the lighthouse-engineer. Engineers have 

 recently realized that by reducing the duration of the 

 flash of light sent out from a lighthouse down to the 

 physiologically permissible minimum, they effect a great 

 economy of luminous energy, i.e. they can with the same 

 source of light, the same lamp, make the ray sent out 

 penetrate to, and be visible at, a very much greater dis- 

 tance than if the flash is made of longer duration, because 

 they concentrate a wide beam into a narrow pencil of 

 intense light. 



