354 Proceedings of Poyal Society of Edinburgh. [sess. 
proper position within the cell, the supporting glass stopper being 
screwed in gently but securely. The cell was then introduced into 
the inner chamber of the tank as shown in fig. 2, and the cork bung 
which carried it pressed firmly home. A thermometer was passed 
through a hole in the cork cover, and adjusted so that its bulb was 
as central as circumstances would permit. The cell leads were 
then connected through the switchboard with the right-hand gap 
of the bridge, the standard resistance coils being joined in a similar 
manner with the other gap. From time to time the tank water, 
which usually had a temperature of about 10° C. at the beginning 
of a series of resistance measurements, was thoroughly stirred ; and 
likewise the sea-water in the cell, by gently raising and lowering 
the upper electrode. After the expiration of the three or four 
hours already mentioned, the sliding electrode was moved up or 
down until the upper of the two lines etched upon the glass tube 
coincided with the index line m (see fig. 1) ; it was then clamped 
(Position A). The slider was then placed in contact with the 
central point of the bridge wire and the induction coil brought into 
action ; then the standard resistance having been adjusted until 
the sound in the telephone had been reduced to a minimum, the 
slider was moved to and fro until it was thought that a true balance 
had been obtained. The position of the slider was now read, frac- 
tions of a millimetre being estimated in tenths; after the first 
reading had been recorded the slider was displaced, sometimes to 
the right, sometimes to the left, and a second and perfectly inde- 
pendent determination of the balance point effected. In an exactly 
similar manner two other determinations were made, and the mean 
of the four, which generally differed but little among themselves, 
accepted as the true value for the bridge reading. The ther- 
mometers placed in the chamber, tank water and resistance box 
were now read ; and immediately after, the positions occupied by 
the cell and resistance coils were interchanged by means of the 
switchboard; a second set of four independent balancings was then 
obtained, the mean value being, as before, accepted as the true one. 
Finally, the total value of the standard resistances was noted. 
After the completion of the observations just described, the 
sliding electrode was at once unclamped and moved upwards until 
the second and lower fixed line etched upon its stem coincided 
