oj Young's Modulus for Glass. 419 



and persistence of the tones obtained from stout and fairly 

 uniform rods of this glass, the low value of a and the absence 

 of a temperature-coefficient, it is admirably adapted for 

 standards of high pitch. The end of the rod on which blows 

 are delivered may be fused, to diminish the risk of chipping, 

 and the tuning effected bv grinding the other end. 



© «/ © © 



All results are given in absolute units. The density at 

 has been determined from selected samples. As it was found 

 to be slightly variable, especially in the case of flint-glass, it 

 is given to only four figures. 



It is perhaps well to point out that the occasional close 

 agreement between the corrected and uncorrected values of 

 n x 21 does not imply approximate uniformity in the corre- 

 sponding rod. This is far indeed from being the case. 



Soft German Glass. 

 1. From Messrs. Gallenkamp & Co. 



Mean n x 21 for eight rods at 14° = 527280 cms. per sec. Of 

 these five of the best were selected for examination. Lengths 

 about 150 cms. p (mean) = 2*508. 



n X '21 observed. a (corrected) cms. per sec. 



527620 525930 



523920 526030 



517240 525940 



525850 526610 



528100 526820 



Mean = 526260 at 6° C. 

 = 526400 at 0° 

 Young's Modulus (adiabatic) or E' 



= 6*95 x 10 11 dynes per sq. cm. at 0°. 

 Eight selected thin tubes of this glass gave a mean value of 

 a x 2/ at 6 C = 525500 cms. per sec. These were not cut up. 

 2. From Messrs. C. E. Miiller k Co. 



Mean product for 12 carefully chosen rods at 14° = 524800. 

 Of these six examined. Lengths about 150 cms. p = 2*507. 

 u x 21 observed. a (corrected). 



529000 525490 



523020 524780 



521270 525400 



526020 524760 



526020 524720 



524580 525100 



Mean = 525050at9° 

 = 525250 at 0°. 

 E / = 6-9lxl0 ll at0°. 



