136 REPORT—1890. 
during the Bath Meeting, the successive curves of which, then exhibited 
by him, he has kindly allowed us to copy. 
In these diagrams the abscissa represent the temperature—in the 
strong curves, that obtained by us, and in the faint, that obtained at 
Kew: the ordinates in each case being the divergence of the 
actual readings from these results. Where crosses occur at almost 
identical temperatures they indicate observations separated by a consider- 
able interval of time ; in no case did less than 20 minutes elapse, whilst in 
some several days. 
Three only of our observations are unrecorded on these charts, and 
in each case, owing to imperfect light, interruptions, &c., these experi- 
ments were regarded as doubtful before their results were deduced. 
The gradual rise of the zero point is clearly indicated; apparent 
discrepancies are probably due to the fact that the Kew determinations 
are less frequent than ours, and as a consequence many of the smaller 
deviations have escaped notice. 
The results show :— 
1. That thermometers whose range does not include 0° and 100° may 
have certain fixed points determined by this method. 
2. That an actual calibration of a mercury thermometer can also be 
readily accomplished. 
3. That the platinum thermometer, properly constructed, may serve 
as a standard by which to trace the changes which may take place in 
mercury thermometers. 
4, That since the readings of the platinum thermometer are indepen- 
dent of the extent of the stem-immersion, it can be conveniently employed 
for the graduation of thermometers partially immersed, as in ordinary 
use. 
We have since calibrated about twenty thermometers by this method, 
and we believe the results to be satisfactory in all cases. 
APPENDIX V. 
On the Absolute Resistance of Mercury. By R. T. Guazesroox, F.R.S. 
The following table gives the results of experiments made since 1882 
on the absolute resistance of mercury. The first eight lines relate to 
experiments in which the resistance of a wire has been found absolutely 
“ “éhd then expressed in terms of the resistance of mercury by direct obser- 
vation. In the next four lines the results of comparisons between certain 
_coils of wire and the resistance of mercury are given. It will be noticed 
that the value found by Lord Rayleigh for the resistance of 100 cm. of 
mercury in B.A. units is considerably in excess of the results of other, 
experimenters. If in obtaining from his value of the B.A. unit expres 
in ohms the value of the ohm in mercury we use ‘9535 instead of 9541, 
Lord Rayleigh’s values 106:24 and 106-21 become 106°30 and 10627, and 
the mean result 106°28 is hereby raised to 106°30. 
The observers whose results are given in the last seven lines, with the 
exception of Lorenz, did not themselves directly compare the results of 
their absolute determinations with the resistance of mercury, but with 
coils usually of german silver, the value of which in mercury units was 
certified either by Siemens or Strecker. 
