172 
MR. SNOW HARRIS ON SPECIFIC INDUCTIVE CAPACITY. 
we may readily determine the full intensity by dividing the charge (8.) and operating 
with ten measures. Suppose the ten measures evinced an intensity of 15°, then the 
intensity due to twenty measures would be 60°, being as Q 2 . We more particularly 
require this, because the full twenty measures would be necessary for the shell-lac in 
order to obtain a decided result, which at the greatest might not exceed in this case 4°. 
Lastly, it is essential to manipulate under a good insulating air, in a dry room and 
with every convenience at hand for warming and thoroughly drying from time to 
time the various insulators, which is best done by means of small heated irons curved 
into half cylinders, and fixed in convenient handles. If these precautions be attended 
to, the electrometers will remain without dissipation for twice or thrice the time re- 
quisite for the experiment, and the result will be found very uniform and invariable. 
Plymouth, 
May 1, 1842. 
