722 Dr. G. W, C. Kaye on the Expansion and 



appear to have been conducted with great care, and the- 

 results are entitled to considerable weight. They have 

 the advantage of not depending on any assumptions as to the 

 effect of temperature and pressure on the refractive index of 

 air at high temperatures *; such effects are of the same order 

 as that due to the expansion of the silica. Randall's final 

 values, reduced as before to the range (t° — 0°) by the aid 

 of Chappuis' and ScheePs values for the interval 0°— 16° are 



given in Table III, 



Table III. 



Temp. (*). 



ilt-k)lh. 











Randall, 



Holborn & Henningt, 



Callendar, " 





1910. 



1903. 



1901. 





— 6 



, 



— (5 





X10 



xio 



xlO 



200° C. 



100 







250 





118 





300 



161 







400 



222 







500 



281 



276 





600 



336 







700 



389 







750 





404 : 402 





800 



"434 







900 



481 







1000 



541 



537 



587 



1100 



641 







In fig. 1 the expansion per unit length (lt — lo)/l is 

 plotted against temperature (t). The results of Randall, 

 Scheel (Zeiss specimen), Dorsey, Chappuis, Holborn and 

 Henning, and Callendar are utilized. 



The excellence with which the curve represents the dif- 

 ferent results will be noticed. The values of Holborn and 

 Henning, and of Randall at high temperatures are in close 

 agreement, as are those of Scheel and Dorsey at low tempe- 

 ratures, and of Scheel and Chappuis at moderate temperatures. 

 It would appear that the curve represents with a considerable 

 degree of accuracy the expansion of clear, transparent, an- 

 nealed silica from "-190° to +11.00° C. The inset gives a 

 portion of the expansion curve on a larger scale. 



* Pulfrich's formula (Zeit. Inst. xiii. p. 455, 1893) has not been tested 

 for temperatures above 100° C. 



t Henning-, Ann. der Phys. xxii. p. 638 (1907) quotes values which 

 when reduced read 132, 267, 402, 537 X 10-6 for the temperatures given 

 in this column. 



