Page:Philosophical Transactions of the Royal Society A - Volume 184.djvu/456

Rh The task of one observer was invariably that of maintaining the potential balance by means of the rheostat, and also inverting the currents at regular intervals. The attention of the second observer was directed to recording the group of transits about each fixed point, the chronograph key being placed at the base of the telescope stand. In the intervals he recorded the times of the revolutions of the stirrer, which were distinguished on the tapes from the temperature records by double marks. He also occasionally recorded the readings of thermometer $$\mathrm{A}$$ (the external temperature), but these were as a rule so regular as to render this observation a matter of form.

Thus, during the progress of an experiment, no notes had to be taken unless some exceptional incident occurred. We believe this to be an important matter during observations of this description, for the mechanical operation of note-taking greatly distracts the attention.

The chronograph required rewinding about every twenty minutes, and in the press of the other observations this was sometimes forgotten. Some of the omissions in the tables are due to this cause. The duration of a whole experiment varied from 40 to 80 minutes, according to the weight of water present and the E.M.F. used.

At the end of an experiment, the chronograph tape was counted and the results tabulated in the form shown in Tables XXVIII. to XXXIII. These six experiments are typical of the rest, and have not been in anyway selected, except that they are the first performed on each weight, in Series II., with different E.M.F.s. MDCCCXCIII.—A.