Electricity on Separation of Parts. 379 
tween the rubber and the points of the conductor in ma- 
chines of the common construction was injurious in its 
effects, not only in causing the dispersion, in part, of the 
electricity excited, but by uselessly wasting the exciting 
surface. Plates were therefore mounted in a very com- 
pact and perfect manner, with three pairs of rubbers pla- 
ced at equal distances from each other; the conductor 
also had three arms, furnished with points a little in ad- 
vance of each pair of rubbers, to collect the electricity in 
the usual manner. The rabbers were not attached toa _ 
surrounding frame, but to brass arms, which, proceeding 
from a socket through which the axis passes, diverged 
from equal distance from each other, towards the periphe- 
ry of the plate. The machine has a very compact and 
neat appearance, and its various smaller parts are contriv- 
ed with much judgment. “" , 
In some comparative experiments made with a plate 
twenty-two inches in diameter, the superiority of three 
pair of cushions over two pair was very manifest. In the 
following table the first column expresses the length in 
inches of the rubbers; the second, the length of the spark 
when two pair of rubbers were used; and the third, the 
length of the spark when three pair of rabbers were on the 
machine. : 
6 inches. 12 inches. 18 inches. 
7 66 14 66 if 91 66 
Denia Hee a 
Bas Pha 18 2 27 a 
oy harass 20 tee re] Paras 
18. Electricity on separation of parts—In the water- 
proof cloths manufactured by M. Mackintosh of Glasgow, 
where two pieces are cemented together by caoutchouc 
dissolved in petroleum, the adhesion is such that when 
the two are torn asunder in the dark, there is a bright 
flash of electric light, similar to that produced by separa- 
ting plates of mica, by breaking Rupert’s drops, or by 
breaking barley sugar, or sugar candy. Upon trying this 
experiment with different substances, it was found that 
‘flashes of light were distinctly produced, by tearing quick- 
ly a piece of cotton cloth. Edin. Jour. 
