Kinetic Theory of Solids,. 35 



2649 gm. The other end of the pipe was similarly secured 

 to a plank which was clamped as rigidly as possible to the 

 beams of a roof. In the case of a hollow cylinder of external 

 radius r 2 and internal radius r x rigidity is given by the formula 



8tt 2 I/ 2 p 

 n Pmtf + rfy' 



The moment of inertia of the plank could be increased by 

 adding weights. 



I. m. p. 9. r 2 . n. 



120-9 ran. 1699gm. 11*4 23° -9014cm. -6482cm. 



With the plank alone, whose moment of inertia was 

 7176000 gm. cm. 2 , the period was -717 sec. ; the moment being 

 increased to 10577000 the period became -881 sec, and with 

 the moment again increased to 20684000 the period rose to 

 1*222 sec. These values give for the rigidity the values 

 89*3 x 10 6 , 87-2 x 10 6 , and 88'6 x 10 6 respectively, the differ- 

 ences being due doubtless to imperfect rigidity in the sup- 

 porting of so heavy a vibrating system. The mean value 

 88*4 x 10 6 at 23° is close enough to the former value 90 x 10 6 

 at 17° to make it pretty certain that the absolute value of the 

 rigidity of lead at 20° can differ but little from 89 x 10 6 

 grammes weight per sq. centim. 



Zinc. — To get a wire of zinc I had a strip about "3 centim. 

 wide cut from a sheet of rolled zinc "3 centim. thick. The rod 

 of square section was then roughly trimmed to circular section 

 with a file, and, finally, by longitudinal scraping while kept 

 revolving it was converted into a fairly uniform circular wire. 



1, 

 73-7 



5-1 



m. 

 36-3 



7-04 



I. 



586500 







OC. 



.18° 



48° 



63° 



82° 



97° 



67° 



52° 



21° 



t/2.. 



.1-338 



1-367 



1-398 



1-446 



1-495 



1-405 



1-382 



1-340 



%/wj 



,1-0 



•952 



•906 



•842 



•784 



•897 



•930 



•997 



Rigidity at 18°, 311 x 10 6 grammes weight per sq. centim. 



Tin. — Again 1 had to make a wire, this time by casting a 

 rod and hammering out to three times its original length. 

 I did not succeed in getting uniformity or true circularity of 

 section, so that a reliable absolute value of the rigidity of tin is 

 not obtainable from these experiments, but the rigidity ratio 

 being independent of the form can be accurately got. 



D 2 



