(126 #. H. Hall— Rotation of the Equipotential Lines 
numbers as observed is too slight to deserve any confidence. 
Estimated R.P. 
Date. Temp. M. C. R.P. at 28°. 
Aug. 22,83. 62° 791-4. 1771 -+7147107-"* 
« 28-2 797°6 1742 +8302 
«“ 28°3 804°6 +1794. +8304 
28°25 801°1 8303 +8290 10-" 
Aug. 23. 28-1 3259 1728 8306 
«“ 28+4 3274 “1702 8289 
«é 27°65 3260 1696 8306 
28-05 3264 8300 +8297 10-" 
Aug. 24. 28°7 5797 1839 ©8391 ; 
« 28° 5833 1842 8310 
«“ 28-0 5875 +1853 8245 
28°27 5835 8315 +8300 10~” 
Aug. 27. 27°25 8626 “1894 8139 
+ 28°35 8690 “1898 8261 
“ 27°95 8636 “1911 8200 
27°85 8651 8200 +8208 X10-" 
Fall of R. P. for 1° fall of temperature equals approximately } per cent. 
On the other hand the decrease in the observed value of the 
R.P. as M rises from 5835 to 8651, though slight, seems to mé- 
strong evidence of an actual falling off in the value of the RP. 
ence drawn from a similar trial made the year before,t that 4 
fall of 1° C. diminishes the R. P. in soft iron about % per cent. 
It is with these experiments as a basis that I have ventured to 
* Phil. Mag., Sept., 1881. + This Journal, March, 1883, p. 218. 
