294 



Prof. W. Thomson on the Elasticity 



[May 18, 



inside (of which the radius of gyration must be, to a very close degree of 

 approximation, the arithmetic mean of the radii of the outer and inner 

 cylindrical surfaces), supported by a thin flat rectangular bar, of which the 

 square of the radius of gyration is one-third of the square of the distance 

 from the centre to the corners. The wire to be tested passed perpendicu- 

 larly through a hole in the middle of the bar, and was there firmly soldered. 

 The cylinder was tied to the horizontal bar by light silk threads, so as to 

 hang with its axis vertical. 



The following particulars show the dimensions of the vibrators of this 

 kind which I have used. 



Towards carrying out the chief object of the investigation, each wire, 

 after having been suspended and stretched with just force enough to make 

 it as nearly straight as was necessary for accuracy, was vibrated. Then it 

 was stretched by hand (applied to the cross bar soldered to its lower end) 

 and vibrated again, stretched again and vibrated again, and so till it broke. 

 The results, as shown in the following Table, were most surprising. 



Remarks. 



a Only forty vibrations from initial arc of convenient amplitude could be counted. Had 



been stretched considerably before this experiment. 

 b So viscous that only twenty vibrations could be counted. Broke in stretching. 



