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covered with cotton is sufficient ; the latter should be well, 
but lightly, covered with silk. Several coils or bundles of 
wire similar to that of the moveable coils, and of precisely 
the like resistance, should likewise be provided. 
The most important alteration which I have made in the 
galvanometer is in adjusting it so that its indications may 
be referred to as an uniform standard. If we could with 
certainty procure magnets of precisely the same power, a 
standard pattern might be agreed upon for the coils, and 
uniform instruments procured. We can, however, readily 
modify the value of the indications in weight, by altering 
the length of the arms to which the scale pans are attached; 
and I propose that the galvanometer be adjusted to a com- 
mon standard, by making a grain weight, supported by the 
10 feet coil, the equivalent to one grain of zinc consumed 
in a single voltaic combination in one hour. 
The galvanometer may, therefore, be adjusted by taking 
a pair of elements. The zinc being weighed, complete the 
circuit with a galvanometer; let the action continue for one 
hour, or any convenient part of an hour, from time to 
time observing and noting down the weights counterpoised 
by the current, and obtaining an average by interpolation ; 
the zinc being weighed, the ratio between the number of 
grains balanced and the number of grains dissolved will be 
ascertained; if this be a convenient number for reduction, 
the galvanometer will be retained in its then state, and the 
observations reduced; or the arms of the balance, which I 
have found to be sufficiently attached to the coil by shell 
lac, may be altered until the indications correspond, — grains 
balanced for grains dissolved. 
This may, perhaps, be more easily rendered intelligible 
by a practical example. A small arrangement of the nitric 
acid battery being used, in which a sheet of platina sur- 
rounded the porous cell, and a narrow strip of zinc well 
