1894 - 95 .] 
Mr J. B. Haniiay on Drops, 
441 
steadily, often quite regular (as at fig. 16), which quickly close up just 
as at the root of a drop, and divide the stream into drops (as at c). 
In this case, as the rod as a whole is gently falling, and all parts 
are equally acted upon by gravity, there is no force pulling the rod 
asunder, yet it divides into drops similar to those formed when 
dropping from a similar tube. The size of a normal drop in oil is 
*4096 C.C., and when dropping at the rate of 10" to a drop the 
volume is increased to *5611 c.c. ; while the drops formed from a 
cylinder of water as above, have a volume of *5470, which shows 
that the determining factor in the formation and parting of a drop 
is surface tension. 
The part played by gravity in determining the weight at which 
a drop will fall consists in its downward pull tending to deform a 
drop which without gravity would be a sphere, as can be seen by 
dropping a non-miscible pair of liquids of equal density one in the 
other, when the drop grows indefinitely into a large sphere. When 
gravity pulls the drop out of its spherical form and forms a cylin- 
drical neck, the contractile force of the liquid surface will not permit 
of this form, but at once starts a constriction which shears through 
the neck and detaches a drop. 
Some experiments which throw light on the function of the neck 
of the drop may be detailed here. If, in forming the rod-like drop 
of water in oil (as at fig. la), we stop the upward motion of the de- 
livery tube while the flow continues, we obtain a formation like 
fig. 2a. The resistance of the oil to the fall of the water causes an 
accumulation at the lower end of the elongated neck in the form of 
a large drop. The long neck may be maintained intact so long as 
a sufficient flow is kept up, but when it becomes long it wriggles 
like something endowed with life, and the surface tension or con- 
tractility causes constrictions to appear and shift from place to place 
without causing any rupture (as at fig. 26). 
When the stream is diminished the contractile force overcomes 
' the power of the stream to keep the tube open, and the tube is 
severed (as at fig. 2c), a new bulb forming higher up ; or if the flow 
be suddenly stopped (as at c?), the entire stem separates into drops. 
The division is seldom very regular, as the neck is in active wriggling 
motion at the moment of rupture. 
In order to study the conditions of parting, water was dropped in 
