of Edinburgh, Session 1885-86. 
651 
when the index of the balance is at zero, the coils hang with their 
planes exactly in the same horizontal plane. In order that the 
weighing may be at all exact it is necessary that the electrical con- 
nections, by means of which the current is led through the sus- 
pended coils, be so made as to interfere as little as possible with 
the sensibility of the balance. This is affected in the following- 
manner : — An insulated copper wire, having its ends tipped with 
short lengths of platinum wire, is run along the lower edge of the 
beam, being firmly lashed to it by well-rosined silk thread. The 
ends of this wire, bent twice at right angles, are so placed that their 
platinum tips dip vertically into one of each pair of the platinum 
cups which are attached to the vertical rods of the suspended coils. 
From the other cup of each pair proceed two similarly tipped 
copper wires which run along the upper edge of the beam, and are 
also firmly tied to it. These wires only proceed as far as the middle 
of the beam, where they are bent first outwards, one on each side of 
the beam at right angles to it, and then downwards, so that the 
platinum tips are vertical. These latter dip into a pair of platinum 
cups attached to two vertical rods which spring from the base board 
of the balance. These rods are placed at equal distances on each 
side of the beam, and are of such length that the platinum cups are 
in line with the central knife edge of the beam, and with their 
edges just a little higher than its level. There are thus in all six 
cups and six dipping wires. Three of these are in line on one side 
of the beam and three on the other. Also the line joining the 
points of each pair of dipping wires is made to coincide with the 
corresponding knife edge; and further, the edges of all the cups are 
in the same plane when the balance is in equilibrium. 
The fixed coils are made precisely in the same way as the sus- 
pended ones, with this exception, that the wooden cylinder with its 
vertical rods is removed. One of these is placed below one of 
the suspended coils (the right hand one usually), and the other, 
having a large central opening for the reception of the supporting 
cylinder and rods of the suspended coil, is placed above the other. 
Each is supported from the base board of the balance by three 
levelling screws, which also serve for adjusting the vertical distance 
between the fixed and suspended coils. This is done by means 
of three distance pieces of brass carefully worked so as to have the 
