MB. H. TOMLINSON ON THE INFLUENCE OF STRESS AND 



Second Day. 

 MAGNETISING solenoid not excited. 



The current used in the trials on both days was throughout fairly constant, the 

 mean deflection of the needle of the tangent galvanometer being 47. The constant 

 of the tangent galvanometer was '3167, therefore the magnetising stress in electro- 

 magnetic units was 



477- X 8-25 X tan 47 X '3167 = 35'21. 



This magnetising stress is a large one, and was, no doubt, sufficient to develop 

 the greater part of the whole magnetism which the wire was capable of receiving. It 

 may be seen that even under such a magnetising stress as the above the internal 

 friction is not much altered ; but, if the first four trials made on the first day be 

 neglected, it appears that the internal friction is on both days greater by about 5^ per 

 cent, when the magnetising solenoid is excited than when it is not. 



Having ascertained thus much, the author next proceeded to determine the effect 

 of an intermittent magnetising stress, but still always in the same direction as before. 



Experiment II. 



One of the little clockwork arrangements used with Professor HUGHES'S induction 

 balance was now put into the battery circuit, so that the latter could be rapidly 

 opened and closed whilst the wire was vibrating, the same battery power being 

 employed as before. In this case the logarithmic decrement was at first fairly 

 constant, and equal to '001442, showing that the internal friction was greater than 

 when the circuit was not alternately opened and closed. After a time, however, as 

 the clockwork began to run down, and the makes and breaks of the current in conse- 

 quence to proceed more slowly, the value of the logarithmic decrement rapidly 

 increased,* and finally became '002719, or nearly double its first value. 



The cause of the rapid increase is shown in Experiment VI. 



