Mr Ronalds on a Pendulum Doubler of Electricity. 828 
Apparatus, 1 ” we find, among many other ingenious contrivances, 
one of a Pendulum Doubler, which we consider highly worthy of 
notice. 
64 In order to shew that he could keep his telegraphic wire con- 
stantly electrified from a very small source of electricity, Mr Ro- 
nalds made the bob of a pendulum perform the part of the centre 
plate of a doubler on Rennet’s or Nicholson’s construction. The 
instrument thus modified, he found convenient, not only for its 
usual purpose, but for all those experiments where a constant 
flow of small quantities of electricity is required to supply what 
is dissipated along imperfect insulation, 
44 The instrument is represented in Fig. 4. of Plate IX., where 
A and B are the two stationary plates, fixed upon glass supports ; 
C is the bob, attached to the pendulum rod D by the glass in- 
sulator e ; its form is a plano-convex lens, and the interior is filled 
with lead ; f is a small cylinder, through which screws pass to 
connect it with C, and to adjust the plane of C exactly parallel 
to the plane of vibration ; g is another insulator, carrying at its 
lower end the bow of wire A, the left side extremity of which, is 
situated nearly in the same perpendicular plane as the end of the 
wire m 3 and the right side is nearly in the same perpendicular 
plane as the end of n ; i is a wire fixed perpendicularly into C ; 
and A another, fixed (perpendicularly to the plane of vibration) 
into the brass cap at the end of the pendulum-rod ; l is a wire, 
screwed into the upper edge of the plate B ; m is a long wire, 
fixed into the lower edge of B, and approaching to within a 
small distance of A, where it is bent at a right angle, and then 
projects in a line perpendicular to the plane of vibration ; n is 
another wire, fixed into the edge of A, and projecting in a simi- 
lar direction (after it has also been bent) ; but the length of the 
projecting part of vn is considerably less than that of n, in order 
that the right side of the bow A, may pass the end of r/z, without 
touching it ; lastly, o is a wire, fixed perpendicularly into the 
base of the instrument. 
44 Since every body may not happen to have seen the revolving 
doubler of Nicholson or Rennet described, I shall shortly state 
the mode of action by which this pendulum doubler produces, 
by the motion of a common clock, a constant flow of electricity. 
It is seen, that when the centre of the bob C arrives opposite to 
