358 
PROFESSOR A. M. WORTHINGTON ON THE 
The vessel consists of two very strong cylindrical bulbs, AB and CD, with rounded 
ends, connected by a tube of narrow bore bent in the manner shown. 
The walls of the bulbs were about 2 millims. thick and the bore of the connecting 
tube was about 2'5 millims. internal diameter. The diagram being drawn to scale 
gives any other necessary information as to dimensions. 
DE is a narrow tube of very uniform bore (2.2 mm.), across which, at F, was sealed, 
with as little disturbance of the bore of the tube as possible, a very fine platinum wire. 
Measurement of the Tension. 
In order to measure the tension of the liquid at any instant, an ellipsoidal bulb T 
filled with mercury, and provided with a narrow graduated capillary stem AE is 
sealed into the bulb AB. This bulb had been previously subjected to various 
measured pressures in an hydraulic press up to GO atmospheres, and the correspond¬ 
ing rise of the mercury in the stem noted. This was found, within the limits of 
observational error, to be proportional to the pressure applied. This rise is due to 
the diminution in capacity of the bulb, which becomes less spherical under the 
external pressure. 
On the other hand, when the surrounding liquid is in a state of tension, it tugs at 
the walls of this bulb and makes it more spherical and of greater capacity, and since 
the bulb is thick-walled and fairly rigid, and the alteration of volume only a very 
small fraction of the whole, it appears quite safe to assume that the enlargement 
produced by a given tension is equal to the diminution of volume that is produced by 
an equal pressure applied over the same surface. 
This instrument for measuring the tension I call the Tonometer. In that actually 
used the relation between bulb and tube was such that a pressure of 1 atmosphere of 
15 lbs. to the square inch, as measured by a Bourdon gauge, gave a rise of 3'296 
millims. The actual observations from which this value was determined were the 
following:— 
Date. 
Pressure 
employed 
(Bourdon 
gauge). 
Resulting’ rise in 
tonometer reading for 
1 atmosphere of 15 
pounds per sq. inch. 
atmospheres. 
millims. 
Nov. 29, 1889 . 
8 
3-25 
99 99 . 
8 
3’375 
’9 99 . 
8 
3-3125 
Dec. 13, 1889 . 
8 
3125 
9 9 9 ? . 
, . 
3T87 
99 9 9 . 
10 
3-450 
9 9 It . 
10 
3-333 
April 29, 1891 .... 
12 
3-333 
Mean . 
3-296 
