410 
MESSRS, T. E. THORPE AND J. W. RODGER ON THE RELATIONS 
colour was stopped entirely at the zone, Pt, Pt'. The second test consisted in half 
filling one limb with water and blowing air from the empty limb through the water 
in the other. Bubbles of air issued tlirough the bore of the capillary tube only; of 
course, if any passage had existed across the zone, its presence would have been 
revealed by a stream of bubbles. 
On one side of each limb of the instrument three fine horizontal lines were etched, 
Z’h on the left limb; m*, /j®, on the right limb. The volumes of the limbs 
between and and between and m‘^ were carefully determined ; these represent 
the volumes of liquid which flow through the capillary. The time taken by the level 
of the liquid to pass from the upper to the lower of either of these pairs of marks is 
the time observed in the experiments. The limb is constricted in the vicinity of the 
marks, in order to give sharpness in noting the coincidence of the meniscus with the 
mark. The shape of the limb between the marks was made cjdindrical rather than 
spherical, in order that the contained liquid might the more readily acquire the 
temperature of the bath in which the glischrometer was placed during an observation. 
It will be seen from the figure tliat the upper ends of the limbs Hh terminate 
within the glass traps T^, T^. These traps admit of slight adjustments of the volumes 
of liquid contained in the limbs, and their use, which is connected with that of tiie 
marks and will be evident at a later stage. During an experiment the levels of 
liquid in the two limbs are continually altering. It will be sufficient here to state 
that the object of these marks and traps is to ensure that at the beginning of any 
observation in a particular limb tbe effective head of the liquid contained in the gfis- 
