228 



Dr. Osborne Reynolds on 



Fig. 2. 



The period of the Analyzer having been thus adjusted 

 to that of one of the periods of free vibration of the 

 structure, the period is ascertained either by adjusting the 

 Analyzer so that the pencil in the ball may oscillate in con- 

 tact with the paper on a chronograph, or by measuring 

 the distance of the ball from the wood on a scale, previously 

 adjusted by aid of the chronograph to give the number of 

 vibrations per minute. 



Extreme accuracy of determining the periods has not 

 so far been an important consideration. The readings on the 

 chronograph were only taken to about io%. But that the 

 Analyzer is susceptible of much greater accuracy is shown 

 by the fact that several different adjustments to the same 

 period in the structure brought the wire into exactly the 

 same position. 



Its power of analyzing complex vibrations is so far 

 unqualified. It was invented for the purpose of determining 

 the period of a particular vibration — in a very stiff iron 

 structure subject to the periodic disturbance of the belts 

 from two engines running at high speed, and the centrifugal 

 action of such want of balance as there might be in heavy 

 pulleys, three feet in diameter, and running at 500 revolutions 

 per minute. The vibration was very slight — nothing more 

 than a slight tremor could be felt with the hand. The 

 periodic disturbances were about 500 per minute, and these 

 came out clearly, but small, in the Analyzer when adjusted 

 to these periods — but the periods of free vibration of one 

 of the members, 720 per minute, caused an amplitude of 



