770 



MR J. D. HAMILTON DICKSON ON 



calculation ; and they led to a probable error of ±'91 micro-volt over a range extend- 

 ing from — 296 to +50, and back again to — 310 micro-volts. 



From this equation (66) we get the equation of the Tait-line, namely 



dE = o9 5 3. 5 62178-5315 

 df = JO 



■ (67) 



Both these curves are shown (the B-curves) on the diagram. 



From the experimental A-curve eleven values of dE/dt were measured directly, 

 the particulars, similar to those in the former case, being given in the annexed 

 Table XL They are plotted along the calculated B-curve of the Tait-line, and verify, 



Table XL 



Deviation 

 in mm. 



h 



h 



Observ. Fract. 



t 



1 

 l dE 



4 

 4 

 4 

 6 

 4 

 4 

 4 

 4 

 4 

 4 

 4 



68 

 43 

 19 



- 8 



- 50 



- 77 



- 97 

 -124 

 -139 

 -163 



60 



29 



6 



- 22 



- 43 



- 84 

 -106 

 -129 



147 

 -168 

 -183 



149 +470 

 20 +150 



145 +434 

 40 +160 



149^ + 434 

 60 +190 



148 +389 

 90 +240 



154 +2971 



150 +320 

 2141 + 4 

 410 +200 

 397 +109 

 200 +200 

 388^ + 186 



80 +200 

 350^ + 260 

 +200 

 330 +305 

 -35 +200 

 299^ + 3431 

 -70 +200 



75J 



48£ 

 241 



- H 

 ■ %H 



- 67 

 911 



- 113 



- 1351 

 -1531 

 -173 



- 3641 



- 2-895 

 -2-334 

 -1-627 

 -0-961 

 + 0-358 

 + 1-265 

 + 2-052 

 + 3053 

 + 3848 

 + 4946 



by a severe test, the assumption that the curve connecting E.M.F. and temperature is, 

 for platinum, a parabola with an inclined axis. As platinum is the only metal for 

 which observations on two specimens were made, it is interesting to compare the two 

 results. The two E.M.F. parabolas and the corresponding Tait-lines are shown, to the 

 same scales, in fig. 16. The vertices of the parabolas are 



Pt(l), t= -56-83°, E + 5012- 



Pt (Calendar), t= -81-35°, E = 12551 • 



The values of dE/dt, when t = o, are respectively -170*08 and — 296"21 C.G.S. units 

 per degree centigrade. The two Tait-lines intersect at t = — 148 '7°, dE/dt = 368 "51. 



