34 Mr. Vince's Observations on the Theory 
orifice and pipes were inserted at the bottom. So far there- 
fore as the theory can be applied when the fluid descends per- 
pendicularly, it appears to be applicable also to the case when 
it spouts upwards. 
At the bottom of the vessel A B C D (Tab. II. fig. 5.) hav- 
ing an orifice r s, I inserted a pipe axyzwv conical at the 
top and cylindrical downwards from it, having the diameter of 
the cylindrical part equal to that of the orifice, and directly 
under it. I then stopped the orifice s r within, and filled the 
vessel, and expected, that as there was now no pipe imme- 
diately connected with the orifice, the fluid would form the 
vena contracta as if there was no pipe, and that the velocity at 
the orifice would be the same as through a simple orifice ; 
whereas I found the velocity to be greater, very nearly in the 
ratio of v"T to 1, the length of the pipe being equal to the 
depth of the cylinder. It appears therefore to flow out with 
about the same velocity as if the pipe had been continued to 
the orifice. The fluid therefore must have flowed from the 
orifice in a cylindrical form, for the pipe was observed to be 
filled. I see no cause which could prevent the vena contracta 
from being formed. I then stopped the pipe at the bottom y z, 
and filled the vessel and pipe, and found the circumstances to 
be exactly the same. 
In order to determine whether there was any pressure of the 
fluid against the sides of the pipes as it passed through in all 
their different situations, I pierced some small holes in them 
at different parts. In the cylindrical pipes, and those in the 
form of increasing cones, the fluid passed by the holes without 
being projected out, or without having the least tendency to 
issue through them ; but in the decreasing cones the fluid 
