132 Progress in Science. (January, 
these lies the knife-edge of a short brass balance-beam, with which is con- 
nected a long index rE. In the ends of the arms of the balance fine glass 
tubes (such as are used for vaccine lymph) are cemented, F F, covered with 
shellac varnish, and bearing at their ends the elder-pith balls,G G. Behind 
this balance there stands upon the same footboard, A a, a wooden support, 
H H, with the scale, JJ. On the balance-arms is cut a screw-thread, by means 
of which the weights, kK K—made in the form of female screws—can be set so 
as to bring the index E to the zero point of the scale. Below the balance- 
beam there is a weight, z, to regulate the distance from the centre of gravity 
to the fulcrum. It is concealed by the fork c, and is therefore represented in 
the figure by a dotted line. If vulcanite is very slightly rubbed upon fur, and 
approached to the elder balls, GG, even at a considerable distance, the maxi- 
mum indication of E is obtained. The electrometer can be combined, in a 
very simple manner, with a condenser. In the wooded foot, 1, the perpen- 
dicular glass rod, m, can be raised or lowered, and fixed at any height desired 
by means of the screw, N. The rod m terminates above in a vulcanite sup- 
port, o, through which passes the brass wire, P, bent at right angle, and bear- 
ing at one end the small brass ball, Q, and at the other the horizontal copper 
disc, R, upon which the condenser plate, $s, can be placed by means of the 
insulating glass handle, Tr. The plates R and s can be unscrewed and re- 
placed by others, as may be requisite. In cases where no condenser is 
required the plate R may be removed, and a simple brass ball fixed in its 
stead. The apparatus is not merely an eleétroscope, but an eleGtrometer. If 
the disc R is replaced by a brass ball connected with any source of eledtricity, 
the ball G will be repelled to an angle a, and the magnitude of the repelling 
force is then proportional to the tangent of the angle of deviation. 
