8 
MR. LATIMER CLARK ON A STANDARD VOLTAIC BATTERY. 
double, and is suspended bifilarly truly central to the fixed coils, the bifilar suspension- 
wires being used to convey the current between the fixed and movable coils. 
The top of the instrument (fig. 3) is furnished with various contrivances for facilitating 
the central adjustment of the coils; these consist of two plates, forming a slide-rest 
movement fitted with verniers, by which horizontal motion can be given to the suspension 
in any direction. The upper plate carries a circular collar, which can be rotated by a 
tangent screw, and is graduated to 360 degrees. Into this collar fits a brass frame, 
Kg. 3. 
carrying two ebonite blocks, on which are two horizontal sliding pieces, diametrically 
opposite to one another, each furnished with a vernier, and terminating interiorly in 
small brass pulleys or rollers, against which the suspension-wires rest, and by which 
their distance apart can be regulated. 
The frame carries a light pulley three centimetres diameter, which supports the 
suspension-wires by means of a silk cord passing over the pulley and attached to the 
wires near the top, so as to ensure an equality of tension on the two wires. The wires 
pass down through the collar and socket to the lower coil. The suspension-pulley 
admits of upward and downward adjustment by means of a milled head screw. 
The electrodynamometer with its telescope and stand was supported on a solid brick 
foundation ; the scale was a metre long, divided into millimetres, and was fixed at a 
distance of 2*7 metres from the centre of suspension. The scale was carefully adjusted 
at right angles to the axis of the telescope. A plate of silvered glass was fixed at the 
back of the large coils and adjusted parallel to them, and upon it was marked the centre 
of the coil accurately determined. When this centre mark, viewed through the telescope, 
was brought to coincide with the cross wires by moving the large coils, and when the 
