THE ROYAL ARTILLERY INSTITUTION. 
15 
The Instrument 
consists essentially of two upright brass cylinders {A.A), revolving on pivots 
{vide Plate, Pig. 1); those at the bottom {BB) being fixed, while the two at 
the top [CC) consist of screws which allow of the cylinders being removed at 
pleasure. They are carefully insulated from one another, but are in electrical 
communication respectively with the two binding screws [BB). On the bed of 
the instrument are two spirit-levels, at right angles to one another, by which, 
with the aid of three levelling screws (EEE), the cylinders may be placed 
truly vertical. Close to, but not quite touching the cylinders, are fixed 
scales, either of equal parts with vernier, or—what is more convenient for 
ordinary experiments—a scale of time, divided to thousandths and ten 
thousandths of a second. On the top, between the two cylinders, is an 
arrangement for suspending the weight; and at the back, an electro-magnet 
for releasing the same, to be hereafter described. 
The Weight 
is of brass, turned with a conical head (Pig. 4). At the base end is screwed 
Fig. 4. 
a piece of steel {A), in which pivots another piece of steel (B); the object 
of this arrangement being, that when the weight is suspended by B, it may 
still swing freely. 
CB is a brass wire, passing through an ebonite tube, and ending in fine 
points; the length of the wire being slightly less than the distance from one 
cylinder to the other, to enable the weight to fall freely between them. 
Two steel arms {E), are placed at right angles to the w r ire, with the object 
of bringing the weight gradually to rest, by entering two Y-shaped springs 
on the bed of the instrument. {Vide Plate). 
