Temperature on the Specific Heat of Aniline. 59 



calorimeter all signs of polarization disappeared, and the in- 

 sulation of the coil was very perfect. 



I will now describe the method ol" conducting an experiment. 



The tank was first brought to the desired temperature, and 

 the experiment was not proceeded with until the tank- tempera- 

 ture had had time to become steady. Freshly distilled ether 

 was then introduced into the silver flask, and dried air passed 

 through it (the stirrer in the surrounding aniline being con- 

 tinually at work) until the whole of the ether was evaporated. 

 The taps connected with the silver flask were then closed, the 

 key inserted in the storage-circuit, the connexion with the 

 Clark cells made, and the rheochord adjusted until the potential 

 difference at the ends of the coil was shown by the high- 

 resistance galvanometer to be equal to that of the Clark cells 

 used. Three or four of these cells were placed in parallel arc, 

 and the files thus formed in series : therefore, when using an 

 electromotive force of 4 Clark cells, we had really in use 12 

 or 16. 



Throughout an experiment the attention of my assistant * 

 was directed to keeping the potential balance as even as 

 possible. I meanwhile had to observe and mark the time of 

 transit across the graduations of the bridge-wire. A reversing- 

 key was maintained at a constant period of oscillation (about 

 twice per second), and as the temperature rose the oscillations 

 of a dead-beat galvanometer mirror (which were viewed 

 through a telescope fitted with a micrometer- scale) steadily 

 diminished, and the moment when they ceased could, to my 

 surprise, be determined with great accuracy. By pressing a 

 key, the time was recorded on the chronograph tape. 



The mercury-thermometer inserted in the walls of the steel 

 chamber was observed at regular intervals, any alteration 

 noted, and a correction afterwards applied to the bridge- wire 

 reading — the value of each division of the bridge-wire in 

 terms of a millimetre of the thermometer-scale being known. 

 The time of each 1000 revolutions of the stirrer was auto- 

 matically recorded on the tape, thus the only notes that had 

 to be taken during an experiment were of the changes of the 

 mercury- thermometer. The chronograph was one of some- 

 what novel construction, for which 1 am indebted to Mr. E. 

 A. Pochin. It was worked by a water motor, had a triple set 

 of recording hammers, and was controlled by an electric 

 clock which was compared at regular intervals with a " rated " 



* I take this opportunity of returning my thanks to Mr. C. Green, 

 Scholar of Sydney College, Cambridge, for his able assistance during 

 these experiments. 



