AND STATICS UNDER THE INFLUENCE OF LIGHT. 
365 
mixture is higher than the temperature of the bath, but always remains constant for 
the same intensity of the same source of light falling upon the gaseous mixture, 
provided that the reaction goes on so slowly that the heating of the system by the 
heat of reaction can be neglected. We are also able from the temperature of the bath 
to calculate the temperature of the gas mixture. Having once determined the 
necessary elements for such a calculation (in a manner given by the author on several 
other occasions)* from the velocity of cooling of the gaseous mixture by the bath and 
from the velocity of heating of the gaseous mixture by the given source of light (at 
the beginning of the induction period), a thermocouple was not introduced into the 
thin glass bulb used instead of the quartz vessel, as it w T as better to make sure that 
during the reaction no vapour of any kind could enter into the gaseous mixture from 
the cement with which the thermocouple has to be fixed in the capillary of the vessel, 
or from the shellac and pitch with which the wires of the thermocouple have to be 
covered in order that they may be protected against the action of chlorine. Indeed, 
the best results, as far as experience goes, w r ere obtained when none of these 
precautions were neglected. 
PART III. 
Experimental Results. (Tables I.-V.) 
In the following tables the experimental data are given : — 
No. is the number of the observation made. 
r is the time at which the observation was made. 
r'-r " is the time between two successive operations. 
77 is the reading of the manometer E of the quartz vessel at the time r, read 
with the cathetometer (38 divisions of the cathetometer scale = 1 millim. of 
the manometer scale). 
tt'-tt" is the rise of the manometer E during the time t"-t. 
is the intensity of the acetylene light, i.e ., the integral intensity of the light 
of all wavedengths contained in the same, expressed in millimetre deflection 
of the galvanometer read on the scale at the time r, including the thermo- 
electromotive force of the Rubens thermopile in the dark ; Th.E.M.F. gives 
the thermo-electromotive force of the Rubens thermopile in the dark, read 
on the scale at the time r. 
i'-th.e.m.f'. gives the intensity of light at the time t'. A correction for the 
deviation of this value from the average intensity of the light during the 
whole time of the reaction can be applied to the velocity constant K, given 
in Tables (II., III., IV. and V.), putting K directly proportional to the 
* See “On Real and Apparent Freezing-Points,” by M. Wilderman, ‘Phil. Mag.,’December, 1897, 
pp. 474, 475. 
