200 SIR WILLIAM CEOOKES ON PSYCHICAL RESEARCH. 



of millions vibrations per second, we have good evidence. That they 

 subserve the purpose of conveying impressions from outside sources 

 of whatever kind to living organisms may be fully recognized. 



As a starting point I will take a pendulum beatmg seconds in air. 

 If I keep on doubling I will get a series of steps as follows: 



The seconds pendulum. 



2 vibrations per second. 



At the fifth step from unity, at 32 vibrations per second, we reach 

 the region where atmospheric vibration reveals itself to us as sound. 

 Here we have the lowest musical note. In the next ten steps the 

 vibrations per second rise from 32 to 32,768, and here, to the average 

 human ear, the region of sound ends. But certain more highly endowed 

 animals probably hear sounds too acute for our organs; that is, sounds 

 which vibrate at a higher rate. 



We next enter a region in which the vibrations rise rapidly, and the 

 vibrating medium is no longer the gross atmosphere, but a highly atten- 

 uated medium, " a diviner air," called the ether. From the sixteenth 

 to the thirty -fifth step the vibrations rise from 32,768 to 34359,738368 

 a second, such vibrations appearing to our means of observation as 

 electrical rays. 



We next reach a region extending from the thirty -fifth to the forty- 

 fifth step, including from 34359,738368 to 35,184372,088832 vibrations 

 per second. This region may be considered as unknown, because we 



