88 ON THE HEAT EVOLVED DURING 
have therefore undertaken a series of experiments 
to ascertain its real character, the results of which 
are, I hope, of sufficient importance to merit the 
attention of this society. 
It would be quite useless to attempt an inquiry 
of this kind, without the assistance of a Galva- 
nometer of very considerable accuracy. Sensible 
of this, I have from time to time, endeavoured to 
improve my own measurers of Voltaism. The 
instrument used in the present investigation is of 
large dimensions and great exactness. It is con- 
structed much on the same plan as Pouillet’s gal- 
vanometer of tangents ; the electricity being car- 
ried by a thick copper wire, bent into a circle of 
a foot diameter. The magnetic needle, six inches 
in length, traverses over a circle of pure brass 
divided by a machine. Its deflections, appreciable 
to 5’, are turned into quantities of electric current 
with the help of a table formed by exact and 
careful experiments. 
Another piece of essential apparatus is a stan- 
dard of resistance to conduction. Mine consists 
of eight yards of copper wire z's of an inch in 
diameter. It is well insulated, bent double to 
obviate any action on the galvanometer, and 
