ON STANDARDS FOR USE IN ELECTRICAL MEASUREMENTS. 97 
attained. Its insulation resistance is good, the loss by leakage being 
about 1 in 1,000 of the total charge per 1 minute. It has been found 
_ possible to compare readily with this standard various mica condensers 
_ having capacities of 1, ‘5, “1, and ‘05 microfarad. The accuracy of these 
_ determinations is about 1 in 2,000. A full account of the construction of 
the condensers and of the method of making the various tests is given in 
_ an appendix by the Secretary, while Dr. Muirhead has contributed some 
- notes on his own condensers and tests. 
Another appendix contains an account of a very careful and interest- 
ing comparison between the standard mercury thermometers of the Asso- 
ciation and a platinum resistance thermometer constructed by Mr. HE. H. 
Griffiths. The resistance thermometer was graduated by means of 
Regnault’s numbers for the vapour pressure of water at various tempera- 
tures between 0° and 100°. 
. The curve of corrections obtained in this way is exactly parallel to that 
given by the Kew comparisons ; there is throughout the range a constant 
difference of 0°-02 between them. This amount is within the limits of 
error on the mercury thermometer. 
The question of the best value to adopt for the dimensions of a 
mercury column having a resistance of 1 ohm has been raised by some 
members of the Committee during the year. There is no doubt that the 
column of 106 centimetres adopted by the Paris Conference in 1884 
is too short. 
After a discussion of the results of the most recent observations, the 
following resolutions were adopted by the Committee :— 
1. The Committee recommend for adoption as a standard of resistance 
sufficiently near to the absolute ohm for practical purposes the resistance 
of a column of mercury 1063 cm, in length 1 square mm. in section at a 
iemperature of 0° C. 
2. That for the purpose of issuing practical standards of resistance 
the number ‘9866 be adopted as the ratio of the B.A. unit to the ohm. 
_ Thus the new unit may be obtained from the B.A. unit by increasing 
it in the ratio unity to ‘9866; or, to put it differently, the specific resist- 
ance of mercury, in B.A. units is taken as ‘9535 x 104, and the length of 
a colamn of mercury which has a resistance of 1 B.A. unit as 10487 em. 
Phe specific resistance of mercury in ohms is ‘9407 x 10%, while the ohm 
8 1:0136 B.A. units. 
_ In conclusion, the Committee wish to ask for reappointment, to enable 
hem to continue the work of constructing and issuing standard instru- 
nents. Of the grant of 501. made at Newcastle only 12/. 17s. has been 
rawn. In order to check any further change in the values of the B.A. 
mits and to render it less necessary to employ the original standards in 
li the comparisons which are made, it is desirable that the Committee 
uld possess three or four copies of the B.A. unit; while, to enable 
aparisons to be made between the new air condensers and condensers 
apacity comparable with a microfarad, a resistance box going up to 
several hundred thousand ohms is required. 
_ The Committee are of opinion that they should be in a position to 
‘chase these resistances ; they therefore recommend that they be reap- 
pointed, with a grant of 100/., that Professor Carey Foster be the Chair- 
man and Mr. R. 'T’. Glazebrook the Secretary. 
1899. It 
