A424 PROFESSOR A. SCHUSTER AND MR. W. GANNON ON A 
Substituting the values which apply to our platinum bowl weighed against brass 
weights, viz., 
the correction becomes 
(i) for difference in temperature + °020 (¢ — 15) millim. 
(ii) 3 ; pressure + °074(76—/h,) _,, 
As regards the silver deposit, the correction amounts to 024 millim. for each gram. 
Neither the accuracy of our weighings nor our knowledge of the equivalent of silver 
render it necessary to apply so small a correction, which would alter our final result 
by only one part in 40,000. 
The balance used was one of CERTLING’s long beam balances, and the sensibility was 
adjusted so that with a load equal to that of the platinum bowl! 1 millim. corresponded 
to one scale division. The bowl was always counterbalanced by the same weights 
before and after the deposit, so that any error in these weights would not affect the 
result. 
To determine the correction, if any, to the weights used in balancing the silver 
deposit, a brass weight of nominal value of 1 gram. was standardised by the Board of 
Trade, and found to weigh 1:000032 gram. The silver deposit weighing always just 
above ‘5 gram., it was sufficient to determine the error of the $-gram. platinum mass 
which was used in all the experiments. Four experiments gave for the corrected 
mass : 499966, 500020, °500032, -499998, or, as a mean, 500004 gram. It was 
therefore sufficient to assume the *5-gram. weight to be correct. 
The Heating Coil. 
The coil in which the electric energy was converted into heat was made of a length 
of 760 centims. of platinoid wire, having a diameter of ‘0345 centims. (29 B.W.G.) 
and a resistance of approximately 31 ohms. The coil used during the first few 
experiments was wound on a frame made of thin strips of ivory. On determining 
the specific heat of that substance we met, however, with a serious difficulty, as it 
was found to absorb a considerable quantity of water, which it gave up again on 
heating. Thus a fresh strip of ivory was found to lose 10 per cent. of its weight 
after heating in an air-bath for two hours. Even coating with shellac will not over- 
come the gradual absorption of water. Having had to discard ivory, we fixed on 
porcelain, and were supplied through the kindness of the Worcester Manufactory 
with strips of that material. The mounting of the frame and wire is seen in fig. 4. 
Four strips of porcelain, 14 centims. long and 1 centim. broad, with 30 notches 
to keep the wire in position, are mounted by fixing their ends in sockets made of brass 
foil, These sockets were connected by stout brass wire. The ends of the platinoid 
