— 169 — 
If the above conditions are exhaustive, ve may assert that 
a drop of liquid will always be of the same size if it is formed 
of the same liquid substance and falls from a solid of the same 
1 size, shape and substance, provided that the barometric ten- 
sion, temperature, and attraction of gravitation remain the 
same and that the growth-time be constant. 
The size of the drops may be most conveniently determined 
by weighing a noted number of them. This gives the weight 
of a single drop. On finding the specific gravity of the liquid 
at the same temperature, the weight of the water is deduced 
whose volume is equal to that of the drop. Hence and from 
the known expansion of water at different temperatures, the 
volume of the water and therefore of the drop is found. 
The whole arrangement employed is shown in Fig. 1. 
The globe A full of the liquid under experiment is invert- 
ed into the cylinder B containing the same. The mouth of 
A is supported by a tripod stand D just in contact with the 
surface of the liquid in B. A and B are carried on a table 
which may be raised or lowered at pleasure. A siphon E 
leads from the reservoir B. and is rigidly held by the clamp 
'F. The longer limb of E from which the liquid flows, is tur- 
ned up at the end which touches a plug of cotton-wool G . 
The sphere II from which the dropping takes place is hung by 
three thin wires from the ring of a retort stand. The upper 
half the sphere is clothed in wool which reaches up to the plug 
G. The whole arrangement is placed upon a board, which is 
separated from the table by six inches if tow so as to diminish 
any accidental vibration. The drops which tall from II enter 
the funnel E aaIiosc loAA'er end is slightly bent so that the 
drops arc throAvn out of the vertical and every upAvard splash- 
ing avoided. The rapidity of the flow through the funnel 
and consequent dropping from II is entirely regulated by rai- 
sing and lowering the table C. The vessel A acts as a regu- 
lator for keeping the level of the liquid in B at a constant 
height. 
The first series of exponents was made with the double ob- 
