ON STANDARDS OF ELECTRICAL RESISTANCE. 175 
know that R= 2 + correction, where N is a known number given at p. 146. 
Hence r, the resistance of the standard coil, may be found in absolute measure 
by the formula 
pan +a small correction ; 
xT 
the value of wT should therefore be nearly constant. 
Thus, on June 23rd, 1863, the experiments were made as follows :— 
At 12" 15™ the resistance of the copper experimental coil was compared 
with that of standard coil “ June 4” taken at 101, and found to be 101:26. 
From 12" 36™ to 12" 45™ the undisturbed position of the suspended mag- 
net was observed, and found to be 590-28 scale-divisions as the mean of all 
the readings. 
The position of the declinometer at Kew at the same time was 7-689 of its 
own scale-divisions. 
From 12" 47" 51*5 to 1" 3" 138 the position of the magnet was again 
observed while the coil was revolving; 104 readings of the scale were taken, 
of which the mean was 930:59. This, when corrected for scale-error, gives 
931-48 as the true reading. The position of the declinometer at Kew during 
the same time was 7-679. The resistance, measured after the experiment, 
was 101-28, 
The number of revolutions was 6300 during the time of observation, so 
that the time of 100 revolutions was 14°464. 
_ By comparing the Kew apparatus with that at King’s College, it appears 
that 1-0 of the Kew scale=19-137 of the King’s College scale. The undis- 
turbed readings at King’s College were found actually to vary very nearly in 
this proportion to those at Kew. 
Hence it is easy to find the undisturbed reading during any given experi- 
ment by comparison with the Kew numbers. 
Thus, for the first experiment on 23rd June we get 
Corrected undisturbed reading .......... 591:54 
emenvcd gondii 2) eae aie tne 931-48 
DBM CCEOD Ottis itm Layee ois ee =-+ 339:94 
Time of 100 revolutions=T ...........4. = 14-464 
STE Ss reign gD tie 2 op ape pete = 4916-90 
Resistance at time of experiment # ...... =e LOL aS 
MOS PA SRO ty, Bey Ott wom = 4979-75 
Three other experiments were made on June 23rd. The result of the four 
experiments was as follows :— 
Ist experiment. Positive Rotation,... T.d.v=4979-75 
2nd he MICRSIVE Sean eck. : T.d.u +... =5071°18 
3rd a IP OSTEO ass ass, os 0% 2 T.6.v=5093°35 
4th ” a T.d.a .... =5007°66 
Mean Positive result .........0ccceceeee 5036-55 ~* 
Mean Negative result..............005005 1+. $=5089-42 
Mean result of June 23rd.......... 5037-98 
Mean result of June 19th.......... 5075:°77 
Mean result of June 16th.......... 5046:18 
ediean; of three days, asigs.scne oejs x0 5053-32 
