208 
elastic fluids through an orifice in a thin plate, was taken 
as the value of the contraction of such orifice, and from this 
co-efficient the highest velocities shown in the several tables 
were deduced. A review of the results of my experiments 
by Prof Osborne Reynolds* led me to doubt the value of this 
coefficient, and to make further experiments with the object 
of determining the maximum rate of discharge from an 
orifice of the best form. 
Five discs of brass had each a hole drilled through its 
centre two-hundredths of an inch in diameter. Equality in 
the size of the holes was accurately determined by means of 
a standard cylindrical gauge. These discs I shall designate 
A, B, C, D, E. 
The disc A was three diameters of the orifice in thickness, 
and was equal to a plain cylindrical tube three diameters in 
length. 
Disc B was the same thickness as A, but the hole was 
coned out on one side to a depth of one diameter and a half 
C was six diameters in thickness, and was coned out on 
one side to a depth of three diameters. 
D had a thickness of twelve diameters of the orifice, and 
was coned out on one side to a depth of six diameters. 
E was eighteen diameters of the hole in thickness, and 
was coned out on both sides to a depth of six diameters, 
which left a plain tube in the centre of the disc six diameters 
in length. 
The wide sides of the coned orifices were equal to two 
diameters, and their outer edges were rounded off to a 
conoidal form. 
The thin iron disc 0 was *007 of an inch in thickness, or 
nearly one-third the diameter of the orifice, which was two- 
hundredths of an inch. One side of the orifice was cham- 
fered to reduce the cylindrical part of the hole as much as 
* Proceedings Mancliester Lit. and Phil. Society, Yol. XXY. p, 55. 
