39 
by me at the meeting at Pontefract, in 1847, and to add 
some suggestions as to methods of applying it, in ascer- 
taining the comparative merits of various forms of the 
voltaic battery. I have also thought that it may be accept- 
able to those who are in any manner interested in the 
subject, that I should, at the same time, explain somewhat 
more fully some of the more practical and important 
deductions from Ohm's law. My ideas may not be found 
altogether original, but Ohm's essay on " The Galvanic 
Circuit investigated Mathematically," is not very accessible, 
being only published in Taylor's Scientific Memoirs, and 
is little, if at all, noticed in the more popular English 
works on electricity and galvanism. 
Some of the methods of ascertaining the constants of 
voltaic combinations which I shall also produce, are similar 
to, or derived from, those of Professor Wheatstone, which 
were published in the Philosophical Transactions, but which 
I fear are not so generally known as is desirable. 
I have, since the date of my paper before alluded to, 
found it more convenient to place the coil of my galva- 
nometer in a horizontal than in a vertical position, as this 
more readily permits the changing the coils without dis- 
turbing the position of the magnet ; and as it is convenient 
for the sake of increasing the dynamic power, and thereby 
the delicacy of the indications of the coil, to use compound 
magnets, of which two are placed side by side thus, UU, 
the axis of the coil being between the two. I also find 
that for most purposes it is advisable to have two coils 
adapted to the instrument, one consisting of about 10 feet 
of copper wire, of No. 20, Birmingham wire gauge, of 
which one foot weighs 27.4 grains, for estimating quantity ; 
and another of 100 feet, of about No. 35, or T 5oth of an 
inch, of which one foot weighs .97 grains, for estimating 
the intensity or electromotive force. For the former, wire 
