698 J. B. HANNAY ON A METHOD OF DETERMINING 
the mercury as a column ; this would fulfil the conditions of a liquid dropping 
from itself, and as there would be no solid to reclaim by adhesion a portion of 
the root of the drop, if Professor GuTurin’s theory were correct we ought to 
have the same weight of drop whatever the rate. This experiment has been 
tried, and the result is that the increase is just as great as when dropping from 
a solid sphere, as in Professor GuTHRIE’s experiments—a result which shows 
that the theory above given does not explain the phenomenon. The following 
theory is more consistent with facts:—There seem to be two causes for the 
increase in the size of the drop with the increase in the rate of dropping ; the 
first being that, as the neck of the drop is a tube conveying liquid into the 
drop, the faster the flow the more liquid will run through that neck in a given 
time, and as there is always an interval between the beginning and the end of 
the breaking of the neck of the drop, the quicker the rate of flow the more 
liquid enters the drop during the act of breaking. The second is that the 
quicker the rate of flow the longer is the time of breaking, because the “stump” - 
of the drop follows the old drop down before finally breaking, so that the 
quicker the rate of flow the more liquid enters the drop during the act of 
breaking, because the tube has a longer lifetime. Concisely stated, then, the 
quicker the rate the greater is the flow of liquid through the breaking neck, 
and the longer does that flow continue. It may not, perhaps, seem of much 
importance which theory is true, since the facts are the same; but in the 
investigation of cohesion the truth or falsity of either of these theories is the 
all-important consideration. It is easily seen that there must be a certain 
weight of drop which is sufficient to break the neck of the drop, and that this 
weight does not vary with the rate, but is always the same for the same width 
of neck, and for this reason may be called a “normal” drop. If Professor 
Guturie’s theory be followed to its legitimate conclusion, there is no such thing 
as a normal drop, as according to him a slow drop is an imperfect one, a part 
of which has been torn back by the attraction of the solid, so that we could 
only have by that theory a normal drop when the rate is infinitely quick, or, in — 
other words, when we have a stream. It is apparent that by this theory the 
breaking weight of a drop cannot be arrived at; but, according to the theory 
above substituted, the drop is normal when its growth-time is infinitely long, 
that is, when there can be no flow into the drop through its neck when breaking. 
If we accept this theory, then we can, from experimental data, calculate the 
size of a normal drop, as we can determine the rate of decrease of weight with 
the decrease of rate, and reduce the rate to zero, when we shall have a normal 
drop. As it was necessary that the temperature should be constant, the fol- 
lowing apparatus was planned for the work :—Fig. 1. The mercury was placed 
in the bulb A, whose contents were/accurately ascertained, and allowed to run 
out at any required rate by the stop-cock ; B, whose handle, C, travelled along 

