Lord Rayleigh on a Statical Theorem. 183 



This calculation leads to the average value 



and there results 



2^6067 ~~ 2 {2/6152 -f y 5Q8 . 3 } , 

 &c. &c. ; 



y 6o67 =04408, 

 3V, 5 = 04489, 

 y 985 . = 0-4589. 



From these experiments it is established that the value of the 



A?/ 

 increase — — in the specific heat of diamond has diminished at 



a red heat and upwards to a white heat, until it has become but 

 the seventeenth part of what it was for the temperature-interval 

 0° to 100°. This increase is now of the same magnitude as the 



value of —7= in the case of those elements which obey Dulong 



and Petit's law. 



Further remarks and deductions will be made for graphite 

 and diamond together, inasmuch as a value for the specific heat 

 of graphite has been obtained almost identical with that obtained 

 for diamond. 



The curve marked diamond in the Table (Plate VII.) exhibits 

 graphically the results of the foregoing experiments ; the plain 

 line shows the results actually observed; the notched line is 

 interpolated from these. 



[To be continued.] 



XXII. A Statical Theorem. By Lord Rayleigh, M.A., F.R.S. 

 [Continued from vol. xlviii. p. 456.] 



SINCE the publication of the paper in the December Num- 

 ber of the Philosophical Magazine, entitled " A Statical 

 Theorem," I have made some tolerably careful experimental 

 measurements in illustration of one of the results there given, 

 which are perhaps worth recording. The "system" consisted 

 of a strip of plate glass 2 feet long, 1 inch broad, and about ^ 

 inch in thickness, supported horizontally at its ends on two very 

 narrow ledges. In the first experiment two points, A and B, 

 were marked upon it, A near the centre, and B about 5 inches 

 therefrom, for which the truth of the theorem was to be tested. 

 When a weight W is suspended at A, the deflection in a ver- 

 tical direction at B should be the same as is observed at A when 

 W is attached at B. 



The weight was suspended from a hook whose pointed extre- 



