1868.] Mr. U. L. J. Ellery on a Pendulum-Electro graph. 459 



4. Charge-measurer apparatus. 



5. Lifting-cradle. 



6. Outer metallic cover. 



7. Charging-apparatus. 



1 . Reservoir of Electricity . — On an octagonal slab of slate I inch thick and 

 15 inches from side to side, is fixed an ordinary Leyden jar, A ; to the inside 

 bottom of this jar, and in connexion with its inside coating, is fixed a pillar 

 of brass tube reaching to about the level of the mouth of the jar ; to the 

 top of this is fixed the support (6) for the moveable part with its mirror. 

 Connected with the pillar, and projecting upwards and outwards beyond 

 the top of the jar, is a branch of metal terminating in a ring (c?), to facilitate 

 charging the Leyden jar. 



The support of the moveable part will be best understood by reference to 

 the Plate, where it is marked d ; it consists of a Z-shaped piece of brass 

 attached to the top of the pillar with a central screw and three set screws, 

 by means of which the surface {e) upon which the moveable part rests may 

 be set quite level. The surface (e) is of polished hardened steel about 1 inch 

 long and \ inch broad, dovetailed into the brass Z-piece. 



2. The Pendulum. — The moveable or sensitive part (P), which may be 

 called the pendulum, has its centre of gravity and point of suspension nearly 

 coincident. It consists, first, of a mirror-frame (/) and knife-edge {g) with 

 counterpoise {h), needle {i) with its counterpoise (j) and balance-screw {k). 

 The mirror, a piece of silvered parallel glass about 1 inch square, is clamped 

 on to its frame by two little clips ; the knife-edge (g) is of hardened steel, and 

 is fixed as nearly as possible in a plane with the silvered surface of the 

 mirror ; the counterpoise brings the centre of gravity of the whole nearly to 

 the centre of the knife-edge. 



The needle is a piece of No. 16 aluminium wire fixed to the back of the 

 mirror-frame, projecting vertically upwards for about 4 inclies from the 

 level of the knife-edge, and terminating in a piece of thin sheet aluminium 

 (a) about H i"ch long and ^ inch wide, bent to a curve of 4 inches radius 

 and fixed to the wire at right angles to the plane of the mirror, and with 

 the chord of its curvature at right angles to the wire itself. The counter- 

 poise to this is found at j ; a small brass wire, screwed, projects down- 

 wards from the frame and carries a small weight, which can be adjusted 

 by screwing up and down the wire so as to obtain the required sensitiveness 

 of the pendulum. The balance-screw (k) is a piece of small brass wire 

 screwed its whole length, terminating at each end in a little capstan head. 

 It is attached at right angles to the frame and perpendicular to the plane 

 of the mirror by means of a small stud (/), through which it can be screwed 

 in order to adjust the whole pendulum to the required verticality. 



3. Electrodes. — Firmly fixed to the slate base are two stout pillars of 

 brass (m, m), |-inch diameter and 20 inches high ; these are connected at the 

 top by a bridge of stout brass {n), to the centre of which a block of ebonite 

 carrying the electrodes (o, o) is firmly screwed. These consist of two seg- 



