Equivalents of Oxygen and Hydrogen. 619 
2. Resistance. 
The working standards were a pair of ten-ohm coils by 
P. Paul, used either singly or in parallel. These are made 
of " eureka " (constantan), and tested between 0° and 25° 
seemed to have no temperature-coefficient exceeding one or 
two millionths. The coils are enclosed in brass cases, with 
terminals at the top. This is not the best pattern of standard 
coil ; but the errors involved in the way of terminals and 
connecting straps would not exceed one or two ten-thousandths 
of an ohm at the most, and are therefore quite negligible. 
The largest current used through either coil was 0*3 ampere, 
the power spent being 09 watt. The heating due to this would 
not cause any thermoelectric error, as the coils are quite sym- 
metrical * but it seemed possible that, with a combination of 
such large thermoelectric power as eureka and brass, the 
Peltier effect might introduce an error. This is so in theory, 
for the current entering at p would heat that junction and 
cool g. Hence a thermoelectromotive force will be set up r 
acting against the current, and the potential difference- 
between p and q will be increased. 
A special experiment was made to test this, by means of a 
potentiometer ; but nothing measurable was found. As art 
additional precaution, however, the brass case was filled w 
paraffin oil. 
The absolute values of the resistances were obtained in the 
following way : — The laboratory possesses two platinum- 
silver standards, of l w and 100 w respectively,, made by 
Nalder Bros., and tested at the National Physical Laboratory.. 
The values are stated to be 
0-99978" at 17°'00. 2170 N. Ph. L. 
99-925 w at 17°'00. 2171 N. Ph. L. 
There were also two eureka coils of l w and 100 w similar 
to the working standards. The eureka l w and 100 w were 
compared with the platinum-silver standards by a Lehfeldt 
comparator. In this comparison the same thermometer was 
used as for the gas-measurement {vide infra), and the tempe- 
rature was within a degree of 17°. (It should be mentioned 
that this measurement was made in a well-built private house, 
where the temperature fluctuations were much smaller than 
in the laboratory.) The temperature coefficient of the 
platinum-silver was assumed to be 0*000247. 
The two ten-ohm working standards were compared with 
each other similarly, and then combined with the l w and 
100 w to make up a "Wheatstone bridge, the l w being shunted 
