of Young's Modulus for Glass. 421 



of these tubes, about 1*3 cm., was rather greater, in proportion 

 to length, than was desirable, but narrower or much longer 

 tube- were not obtainable. p =2°525. 



X '21 observed. 



a (corrected). 



542380 



539820 



539690 



539350 



540570 



539850 



541420 



539560 



Mean a at 9° = 539650 cm. per sec. 

 at 0°= 539850. 

 E'=7-36xl0 n at0 c . 



''Soft" Jena Glass. 



Stout tubes, somewhat narrower than the foregoing, of 

 length about 111 cms. /o = 2'199. 



n x '21 observed. 



a (corrected) 



533120 



535370 



535650 



535650 



531510 



535200 



527800 



534860 



Mean a at 7° = 535270 cm. per sec. 

 = 535400 at 0°. 

 E' = 7-16xlO n atO°. 



Flint Glass. 



From the Whitefriars Glass-works. Mean product for 

 ten thin rods at 3° = 109910. Lengths about. 91 cms. 

 p ( mean) =3*164. 



n x '21 observed. a (corrected). 



405360 408740 



410400 409550 



412680 409820 

 407300 409780 



410510 409610 



Mean a = 409500 cm. per sec. 

 Not changing with temperature. 

 E / = 5-30xl0 11 at0°. 



For this glass, the value of E' depends greatly on the 

 amount of lead contained. For example, in two other 



