274 MR. E. H. GRIFFITHS ON THE LATENT | 
Although, of course, I had, when commencing these experiments, no exact know- 
ledge as to the comparative values of the terms, some preliminary observations 
enabled me to form a rough estimation of their magnitudes and consequently of the 
degree of attention which should be devoted to their accurate measurement. 
Section [1V.—THE MernHop or MAINTAINING THE SPACE SURROUNDING THE 
CALORIMETER AT A CONSTANT TEMPERATURE. 
I have, in Paper J., given an account of the apparatus employed for this purpose, 
and full details and plates will be found on pp. 374-378 (cbid.). 
In order, however, to give a general idea of the arrangements, and to save the 
reader the trouble of reference, I will here quote the brief description given in the 
abstract of that paper :—‘ The calorimeter was suspended within an air-tight steel 
chamber. The walls and floor of this chamber were double, and the space between 
them filled with mercury. The whole structure was placed in a tank containing about 
20 gallons of water, and was supported in such a manner that there were about 
three inches of water both above and beneath it. The mercury was connected by a 
tube with a gas regulator of a novel form, which controlled the supply of gas to a large 
number of jets. Above these jets was placed a flat silver tube, through which tap- 
water was continually flowing into the tank, all parts of which were maintained at an 
equal temperature by the rapid rotation of a large screw. Thus, the calorimeter may 
be regarded as suspended within a chamber placed in the bulb of a large thermometer 
—the mercury in that bulb weighing 70 Ibs. A change of 1° C. in the temperature 
of the tank-water caused the mercury in the tubes of the regulating apparatus to rise 
about 300 millims. Special arrangements were made by which it was possible to set 
the apparatus so that the walls surrounding the calorimeter could be maintained for 
any length of time at any required temperature, from that of the tap-water (in summer 
about 13° C., in winter 3° C.) up to 40° C. or 50° C.” 
I think the above summary, together with the section on Plate 4, will convey a 
sufficient idea of the apparatus. 
Since 1892, I have made certain improvements, which I will briefly describe. 
During my J. experiments the range of temperature was from about 14° C. to 26° C. 
In subsequent experiments when I have required to use the apparatus at higher 
temperatures, it was found that the oscillations in temperature became serious, in some 
cases amounting to 35° C. This was due to the temperature lag of the large mass of 
mercury, so that when the gas was lowered by the action of the regulator the resulting 
in-flow of cold water lowered the tank temperature before the mercury had contracted 
sufficiently to again heat the in-flow. In Paper A. I have described as follows the 
arrangements made to meet this difficulty :—‘ As now arranged, when working above 
temperatures about 20° C., a small motor acts as a heart, and, the tap-water being 
shut off, pumps the tank-water itself round through the silver tube placed above the 
