[ 338 ] 
to the rubber fhould likewife ' have its conducing 
and nonconducting fide. For this purpofe, it may 
be neceflary to employ baked wood, and to cover 
the potter ior half with tinfoil. The place of ex- 
citation will be thus fufficiently fupplied with eleftric 
matter i and the cylinder will not be robbed of 
a part of the excited fire, before that fire has made 
a revolution with the glafs. 
By attending to the place where the excitation is 
effected, it mutt appear evident, that the amalgam 
is only to be laid on the pofterior part of the cuflfion ; 
its prefence, indeed, would be ufelefs, if not in- 
jurious, in any other fituation. It will, however, 
be found fomewhat difficult to confine the pure 
amalgam to the pofterior part of the rubber ; but if 
it is mixed with a little hair-powder and pomatum, 
it pretty perfectly keeps its place. The ftrewing 
the amalgam thus prepared on the glafs, as it revolves, 
is perhaps the beft method of applying it ; as, by 
that means, it is in a great meafure prevented from 
patting on to the nonconducting fubftances that are 
placed before. Should any of the amalgam be car- 
ried forward by the revolution of the glafs, it fhould 
be carefully removed. The neceffity of keeping 
that part free from conducting bodies cannot be too 
much infifted on ; and, when frefh amalgam is ap- 
plied as before mentioned to the proper part of the 
rubber, the flap fhould be held down during half 
a dozen turns of the machine, left it might collect 
feme of the amalgam before it is properly fixed. It 
is a probable conjecture, that, when the flap of 
fllk is covered with amalgam, part of the amalgam, 
$vhich is not immediately fubfervient to the excita- 
tion. 
