68 



Royal Society : — 



I used as vibrator in each case a thin cylinder of sheet brass, turned 

 true outside and 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 cor- 

 ners. The wire to be tested passed perpendicularly 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. 













Moment of 



Cylinders. 



Outer diameter. 



Inner diameter. 



Mean radius. 



Weight in 

 grammes. 



inertia round 

 axis in 

 gramme- 

 centimetres. 



No. 1 



15*3 centims. 



14*8 centims. 



7-525 



527-92 



29894 



„ 2 



15-3 



14-8 „ 



7-525 



523-45 



29641 



» 3 



10-295 „ 



9-79 „ 



5-021 



360-54 



9089 



»i 4 



10-3 „ 



9-81 „ 



5-027 



726-40 



18357 



» 5 



10-25 „ 



9745 „ 



4-999 



718-36 



17952 



» 6 



10-295 „ 



9-805 „ 



5-025 



342-45 



8647 





Length. 



Breadth. 



Weight. 



Moment of inertia 

 round axis through 

 middle, perpendi- 

 cular to length 

 and breadth. 



Bar 1 

 » 2 



24-03 centims. 

 24-11 „ 



•965 centim. 

 •95 



38-955 grms. 

 46-68 „ 



1877-5 

 2255-5 



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 vi- 

 brated. 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 fol- 

 lowing Table, were most surprising. 



Length of 

 wire, in 

 centime- 

 tres, 



I. 



Volume, in 

 cubic cen- 

 timetres, 



V. 



Density. 



Moment of 

 inertia of 

 vibrator, 



W£ 2 . 



Time of 

 vibration 

 one way 

 (or half- 

 period), 

 in seconds, 

 T. 



Rigidity, in 



grammes weight 



per square 



centimetre, 



g-T*Va 



Substances. 



60-3 

 3049 

 237-7 

 248-3 



1-1845 

 2351 



2-764 

 7-105 



31771 

 31896 



1-14 

 4-31 

 4-76 

 5-456 



241X10 6 

 359-6X10 6 

 410-3X10 6 

 354-8 X10 6 



Aluminium a . 

 Zinc b . 

 Brass. 



>> 



Remarks. 

 R 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. 



