310 



Mr. A. E. Tutton. 



determinations for all the three directions ; the mean, however, can be 

 regarded with the fullest confidence as expressing the true coefficient 

 at 0°. The agreement of the values for the constant b is really 

 remarkable, considering the extreme smallness of the constant, and is 

 to be attributed to the perfection of the polished surfaces of the nickel 

 block ; the mean undoubtedly expresses the true semi-increment per 

 degree of temperature. 



Calculated Expansions. 



Diminution of thickness 



Expansion of tripod 



Expansion of cobalt 



of air-layer. 



screws. 



block. 



/-2V2. 





For t 2 - t x . 



For * 3 - t x . 





- w 



f 0-0025690 



-0056138 



-0060802 



-0125913 



I 0-0086492 



-0182051 



{ 26904 



55352 



65423 



126876 



92327 



182228 



L 25559 



55022 



63120 



126710 



88679 



181732 



22836 



48789 



56324 



112972 



79160 



161761 



\ 24804 



50560 



58150 



114269 



82954 



164829 



[ 26216 



52431 



60980 



• 118065 



87196 



170496 



f 18833 



37403 



43540 



84246 



62373 



121649 



< 18472 



36748 



44799 



86203 



63271 



122951 



L 18669 



■ 



36781 



44653 



• 



85905 



63322 



122686 



Calculated Linear Coefficients of Expansion. 



f. 



<p. L . 



a. 



b. 



f 0-000 156 93 



0-000 000 092 3 



12 -9740 



-000 012 10 



0-000 000 0071 



< 155 10 



98 9 



12 -9743 



11 95 



76 



L 153 79 



1061 



12 -9742 



1185 



82 



137 52 



88 6 



11 -5876 



11 87 



76 



< 141 21 



691 



11 -5878 



12 19 



60 



[ 141 89 



65 4 



11 -5882 



12 24 



56 



105 65 



45 3 



8 -5981 



12 29 



53 



1 103 95 



48 3 



8-5983 



12 09 



56 



[ 104 77 



42 9 



8-5983 



1218 



50 





Mean values 



-000 012 08 



000000006 4 



The mean coefficient of linear expansion, a + bL of pure cobalt, 

 between 0° and f, is thus found to be 



0-000 012 08 + 0-000 000 006 4/, or 10- 8 (1208 + 0-64/). 



The true coefficient a of linear expansion at t\ or the mean coefficient 

 between any two temperatures whose mean is t, is a = a + 2bt, that is 



0-000 012 08 + 0-000 000 012 8/, or 10- 8 (1208 + 1'28/). 



