ON THE SPECIFIC RESISTANCE OF MERCURY. 
181 
used. A thermometer lay beside the tube during the measurement, so as to give the 
temperature t. After the measurement, the mercury was blown out into a small 
crucible and weighed. Care had to be taken not to leave behind minute globules, 
which, owing probably to the small portion of the tube unoccupied by mercury during 
the measuring becoming damp from the air of the room or from the fingers, tended to 
adhere to the glass near the ends. 
In three cases (No, 5 as above mentioned and Nos. 3 and 9) the mercury weighed 
and measured was not that of which the resistance was taken. 
No. 3 was done before it occurred to us that there might be an advantage in carry¬ 
ing out both operations with the same filling, and in No. 9 about one-tenth of the 
mercury was spilt accidentally and had to be replaced. 
The equality of the arms of the balance used for the weighing was tested. The 
weights were compared among themselves and found to be free from appreciable 
error. 
The terminals were composed of L-shaped pieces of ebonite, hollowed out in the 
manner shown (about full-size) in the figure. Each end of the tube was furnished 
with a short length of thick rubber tubing, by which the aperture between the glass 
and the ebonite was closed air-tight. As a further precaution, the space at c c beyond 
the rubber was filled up by pouring in melted paraffine wax. 
After the terminals w T ere fitted the tube was again aspirated with dry air through 
tubes in corks inserted at a a, and then filled with mercury, which was poured in to 
one terminal and allowed to run slowly through to the other till it stood at a con¬ 
siderable height, represented by d d, in both terminals. The tube was then placed 
in a wooden trough and covered with ice. Our reason for using vulcanite terminals 
rather than glass ones was the fear that under the influence of the ice moisture would 
collect on the portion of glass above the mercury and serve as a conductor. We 
certainly avoided all difficulty of this kind by using vulcanite. On the other hand, 
we probably increased a difficulty which would have existed in any case, namely, that 
of getting the temperature of the portion of the tube which was within the terminal 
