362 MB. A. E. TUTTON ON A COMPENSATED INTERFERENCE D1LATOMETER. 



SERIES 2. 



Thickness of black glass block, Lt, = 12'956. 

 Length of screws above table points, I = 13'221. 

 Thickness of air-layer, d 0'265. 

 Temperatures, t, = 6'0, t. 2 = 69'0, t, = 119 'i. 



2 , = 63. t A t l = 113-1. 

 Pressures, I, = 743, b, = 745, b 3 = 746'5. 

 Number of transited bands, f, = 3'24,/ 3 = 5 '19. 

 Correction, + 0'05, + O'OS. 



Corrected number of bands,// = 3'29,/ 3 ' = 5'27. 

 Wave-length of light employed, X = 0'0006562, X = 0'0003281. 

 Increase of thickness of air-layer, // 1 X = 0'0010795. /,'i\ = 0-0017291. 

 Elongation of screws, 



I 



10- 9 (8600 + 4-56^- 



10- 9 8600 + 4-56 



(t, f,) = 0-0073052. 

 (t a t,) = 0-0132850. 



Expansion of black glass block. 



LL - Lrf! = 0-0073052 0'0010795 = 0'0062257. 



L< 3 L^ = 0-0132850 0'0017291 = 0'0115559. 

 = O'OOO 093 804. <j> = O'OOO 000 066 894. 

 L = 12-95514. 



a = O'OOO 007 240 7. I) = O'OOO 000 005 163 6. 

 The two results are compared below, and their mean extracted : 



Mean values, a = O'OOO 007 257 0. b O'OOO 000 005 203 9. 



Hence the mean coefficient of expansion a + bt of the black glass of the crystal- 

 covering-discs, between and t is 



O'OOO 007 257 + O'OOO 000 005 2Qt, 



or 10- 9 (7257 + 5'2). 



The true coefficient of expansion at t, or the mean coefficient between any two 

 temperatures whose mean is t, a = a + 26i, is 



a = O'OOO 007 257 + O'OOO 000 010 4, or 

 = 10- (7257 + 10-4*). 



