298 MR. E. H. GRIFFITHS ON THE LATENT 
70 units. It would thus appear that R I exceeds Professor ScHustTER’s standard by 
48 units, 7.e., by about 0°0007 volt. It must, however, be remembered that between 
these comparisons the cells had been subjected to several transits by railway. | 
Measurement of Time. 
The chronograph was controlled by the electric clock described in Paper J. (p. 414). 
The clock has remained untouched from July 16th to the present day—November 18th, 
and during that time it has gained 12 minutes, z.e., a gaining rate of about 1 in 15,000. 
The gain has been regular throughout the interval, the clock being singularly indifferent 
to small changes of temperature. I therefore consider that the measurements of time 
require no correction. 
Section [X.—TuHeE ResuLtts oF EXPERIMENTS IN WHICH EVAPORATION WAS 
PROMOTED BY THE PASSAGE OF A GAS. 
I have hitherto referred to the experiments I describe in this section as “ pre- 
liminary” for want of a better name; but I had originally hoped that the method 
would have given satisfactory results. Although these experiments have had but 
little influence on my conclusions, I will briefly describe them, as I am yet at a loss to 
account for their comparative irregularity. 
Dry air, or other gas, was forced in a continuous stream through the water 40 be 
evaporated ; the cooling thus caused was balanced as before described, and the weight 
of water evaporated determined by the increase in weight of drying bulbs. I wished 
to adopt this method, because by adjusting the flow of air the rate of loss of heat 
could be (by proper arrangements) regulated with nicety, and the thermal balance 
maintained with great accuracy. When water is made to boil by diminished pres- 
sure, the regulation of the cooling presents many manipulative difficulties that I was 
anxious to avoid. 
The experiments were conducted as follows. About 20 cub. centims. of water were 
placed in the flask F (Plate 6, fig. 1),* the water force-pump set going, and the air 
first passed through the H,SO, bottles and “tower” S, then through the U-tube 
and drying tower P—both containing P,O;. It then passed through the 3-way 
tap (T,) into the 30-feet copper coil (C,) in the tank water, thus attaining the tem- 
perature 6, of the tank, and after traversing the immersed tap T;, bubbled through 
the water in the silver flask. The air and vapour now rose up through the 18 feet of 
silver coil (C,) within the calorimeter, passed out through the 4-way tap (T,), which 
was opened in such a manner as to direct the air current into some H,SO, bulbs (not 
* This figure is diagrammatic only, and conveys no idea of dimensions or actual position. For example, 
the coil C, surrounded the steel vessel, and the 4-way tap T, was on the same side of the apparatus as 
the tap T,. The pipes, &c., crossed and re-crossed each other in such a manner as to render any direct 
representation. impossible. The drying bulbs and connections are not indicated in the figure, as they 
were afterwards replaced by the condenser (B) and manometer (M,). 
