I- Mil H. TOML1NSON ON THE INFLUENCE OF STRESS AND 



The Effect on the Interned Friction and on the Torsional Elasticity produced by 



an Electric Current. 



Experiment XVI. 



Some experiments made in the year 1880* had seemed to show that, unless an 

 electric current was very powerful, its influence on the torsional elasticity of iron 

 and copper was very nearly, if not quite, nil ; and even in those cases where, apparently, 

 slight changes were wrought by powerful currents the results were such as to leave 

 the question undecided as to whether these changes might be due, not directly to the 

 current, but rather to the consequent heating. Accordingly the author determined to 

 dispense with powerful currents, and to endeavour to compensate for the lessening of 

 the current by increasing the accuracy and number of the observations. The 

 following were the arrangements : 



The clamp which secured the upper extremity of the wire was provided with a 

 terminal screw, by means of which connection was made with one pole of a battery of 

 five cells of the LECLANCHE type.t To the bar of the vibrator attached to the lower 

 extremity of the wire was soldered a rather fine sewing needle, which, hanging 

 vertically downwards in a line which was a continuation of the axis of the wire, 

 dipped with its point into a cup filled with mercury, whilst a caoutchouc-covered 

 connecting wire, passing from the cup through a key and a tangent-galvanometer to 

 the otjier pole of the battery, served to complete the circuit. It having been 

 ascertained that the rotation of the fine point of the needle in the mercury did not 

 appreciably increase the logarithmic decrement, the effect of the current .on the 

 internal friction and the torsional elasticity of wires of nickel, iron, and tin was 

 investigated. As the lengths of the wires used were in all cases more than 

 600 centimetres^, and the diameters comparatively small, the strength of the current 

 did not exceed 0'30 ampbre. It will be hardly necessary to enter further into 

 details, since these experiments resemble very closely those already described, when 

 the effect of longitudinal magnetisation was tested. Suffice it that the examination 

 of the wires occupied several days, and the final conclusion arrived at was that when 

 the current was maintained constant there was no effect on the internal friction or on 

 the vibration-period produced by it apart from what might be expected from the very 

 slight rise of temperature resulting from the passage of the current, which rise could 

 not in any case have equalled 1 Centigrade. 



* ' Phil. Trans.,' 1883 (vol. 174, Part I). Experiments 24 and 26. * 



\ The current yielded by this battery did not vary so much as 5 per cent, during the whole of the 

 period of experimenting. 



J The apparatus here used was described in the author's first memoir on Internal Friction. 



This could be calculated within a sufficient degree of approximation from data furnished br Mr. J. T. 

 BOTTOMLET ('Nature,' Sept. 25 and Oct. 2, 1884). 



