420 
MESSRS. T. E. THORPE AND J. W. RODGER ON THE RELATIONS 
however, was falling too rapidly to admit of these observations, both limbs were put 
under the same pressure before the level fell to the mark P. 
To take an observation in the left limb, precisely similar operations were gone 
through. The volume of liquid Avas first adjusted by bringing the level in the right 
limb to Since, under ordinary circumstances, the left limb observation was taken 
at the same temperature as the previous one in the right limb, and from the fact 
that the limb is expanded below the mark sufficient time is given to the observer 
before tbe meniscus passes from to k^ to enable him to begin the observation in 
the left limb, the cocks, Z, Z', having remained undisturbed from the beginning of the 
right limb observation. The working volume, k"^ is, as already stated, slightly 
less than k^ Hb This was necessary because at high temperatures during the flow 
from the right limb a small but appreciable loss of liquid by evaporation took place, 
chiefly from the left limb, which was, of course, at atmospheric pressure. It was 
necessary, therefore, in order that observations might be taken at the same tem¬ 
perature in either limb, that the working volume in the left limb should be the 
smaller. 
Care had to be taken not to make the difference of the volumes too great, for in 
order that the right limb observation may be taken after a left limb observation, the 
difference betv/een the volumes must be made up by the expansion of the liquid in 
attaining the next higher temperature of observation, and in some cases this tem¬ 
perature interval is small—some 5° or so. 
Having taken the necessary readings in the left limb, the pressure was equalised 
on the two limbs before the level of liquid fell to ¥ and the bath was now raised to 
the next temperature of observation. 
To obtain temperatures between 0° and the atmospheric temperature, hot water, 
and, when necessary, ice were introduced into the outer compartment of the bath, 
and after several trials the quantity of boiling water needed to effect a given rise of 
temperature, and the quantity of ice which had to be added from time to time in 
order to maintain it constant, were ascertained with considerable precision. After 
the temperature of the bath had become steady and the liquid in the glischrometer 
had had time to acquire it, the head of liquid was adjusted and the observations 
taken as already described. 
To maintain the temperature just above that of the atmosphere small quantities 
of boiling water were from time to time introduced into the outer compartment of 
the bath; for higher temperatures up to 100°, the water-bath was heated by small 
Bunsen burners. 
Temperatures above 100° were obtained by the use of the glycerin bath, the water 
bath containing the glischrometer being allowed to cool to about 40°, and the 
glischrometer then transferred to the glycerin bath, Avhich had been previously warmed 
over a steam tray. The glycerin bath was heated by a large Bunsen burner with a 
spreading flame. 
