440 
Proceedings of Royal Society of Edinbm^gli. [sess. 
densities and viscosities, and oils were allowed to drop up through 
water, so that by the slow parting of such drops the method of 
parting could he investigated. 
As the experiments of dropping water in pure olive oil gave very 
constant results, I will use the numbers obtained in this way in 
illustration of my conclusions. 
The conditions were studied by dropping distilled water from a 
tube 5*9 mm. internal and 7 '6 mm. external diameter, at a tem- 
perature of 20°, in saturated air and in pure olive oil. It was 
clearly seen when dropping in oil that the rupture of the drop from 
the end of its supporting column was an operation taking some time, 
and from the moment the neck began to narrow till it parted was 
about 2*8 seconds. When the rate was quicker there was very 
little difference in the time taken to complete the rupture, and at the 
highest rate at which observations could be made it was not over 
3 seconds. Then it was also seen that the root of the drop left 
behind was always the same size no matter what the rate. The 
stump was measured by viewing with a cathetometer, and the 
following numbers obtained when dropping oil in air : — 
Growth Time of Drop. 
Length of Stump. 
Mean of Ten Observations. 
12 " 
78 ° 
7 - 5 " 
77 ° 
4 - 3 " 
78 ° 
1 - 9 " 
79 ° 
0 - 6 " 
80 ° 
0 - 3 " 
78 ° 
From this we see that all the liquid which flows down during 
the rupture of the neck passes into the drop, and that the neck parts 
at the highest point. 
The cause of the rupture of the neck was then studied, and it was 
found that it was due to two causes — namely, surface tension and 
gravity. This can be proved in several ways. When water is 
delivered in a solid stream into oil from a tube of the same diameter 
as that from which the drops were produced, and if, during de^ 
livery, the tube be raised at a suitable speed, then the water can 
be delivered into the oil as a straight rod (as in fig. la). But at 
intervals along this rod there rapidly form constrictions, generally 
somewhat irregular ; but when the stream has been delivered very 
