AT THE BOUNDARY OF A LIQUID IN MOTION. 
567 
The bulb had a capacity of about 850 c.c., and was fixed to a wooden frame to 
prevent breakage; this was screwed to the edge of a table. The water bath was 
eventually abolished, and the temperature of the water read off at intervals during 
each experiment as it passed through a broad tube, into which the capillary tube 
opened. The temperature of the water was thus read off immediately after it had 
passed the important place, and by taking readings at equal intervals while the bulb 
was emptying, a very accurate estimation of the average temperature could be 
obtained. Below the temperature tube was a three-necked Wolff’s bottle W ; the 
second neck was connected to a large carboy C, and the third could be put into 
communication with the atmosphere. The carboy was connected to a three-way tube, 
the branches of which went, one to the Wolff’s bottle, one to an air pump P', 
worked by the water supply, and one to the gauges S and M. The gauge S con¬ 
tained sulphuric acid, and M contained mercury. The latter was only used for the 
experiments in which higher pressures were employed.The bulb was filled by dis¬ 
connecting the joint B, and putting the lower orifice of the temperature tube in 
communication with c, the tube joining C and W being stopped. P was then put to 
the pump, and the water in W sucked up. When the bulb was filled, B was again 
connected, the carboy exhausted by putting P' to the pump, and the tube from 
C to W opened. The pump was worked till the recjuisite pressure, as shown by the 
gauge, was reached. 
The apparatus was then left till the temperature had become constant after the 
disturbances produced by exhausting, and the height of the gauge read off by a 
kathetometer. The pressure could be adjusted to within a millimetre or less by 
regulating the pumps, and small differences in corresponding experiments, were given 
by the readings of the kathetometer. The correction to be applied to the times 
of flow for a given small difference of pressure, was determined by observing the 
actual times of flow for pressures whose difference was considerably greater than that 
in the experiments to be compared, and keeping all other things unchanged. The 
small pressure correction could then be accurately estimated from the result of this 
auxiliary experiment. As before, the experiments were to be only comparative, and 
the pressure was allowed to fall during each observation. Any change introduced by 
this would affect the tube equally whether plain or silvered. In order to show the 
method of working and the degree of accuracy obtained, a complete account of 
an experiment is given in detail. 
* All permanent joints, corks, &c., were thickly covered with marine g'lue, and were quite air-tight. 
