Theory of the Pneumatic Paradoc. 307 
lateral hole, the jet rose vertically, as in the preceding case, to the 
height of forty seven inches. The end of the tube was then 
unstopped, and the jet becoming inclined at an angle of forty or 
forty five degrees with the horizon, attained the height of sixteen 
or seventeen inches above the level of the tube, and the distance 
of thirty inches before descending to the same level. The force 
of the jet was not apparently diminished by inclining the reser- 
voir, so as to give the tube an ascending or descending direction. 
By diminishing the head of water, a corresponding diminution 
was produced in the height of the jet. 
Experiments similar to the two last described, with the excep- 
tion of the substitution of drawn leaden tubes, both with and 
Without an ajutage, and of the same dimensions with those em- 
ployed by Bossut, gave results not materially different from the 
preceding. The tubes were one eighth of an inch in thickness, 
which interfered with the natural direction of the jet,and somewhat 
diminished its height, and it was almost impossible to pare away 
the lead about the holes sufficiently to obviate this obstruction, 
Without impairing the cylindrical shape of the tubes. Cn this 
account, therefore, and because of the imperfection of their inte- 
rior surface, experiments made with them are less to be relie on 
than those which I have already described. They were suffi- 
cient to show that mere difference of size produces no material 
discrepancy of results. 
The foregoing experiments demonstrate a pressure against the 
inner surface of horizontal and inclined tubes, independent of 
that which arises from the column of water contained in them. 
Of this pressure the lateral jet, though it proves its existence, 
cannot be regarded as a measure. Its oblique direction, and t 
consequent obstruction presentéd by the thickness of the tube, 
together with the diminution of pressure arising from the expen- 
diture of the jet itself, prevent it from reaching the height due 
to the actual lateral pressure exerted by the flowing water, when 
the hole is closed. ; Z 
Experiment LV. In order to determine whether lateral pressure 
takes place in vertical descending tubes also, 1 procured a cylindri- 
cal vessel of tinned sheet iron, thirteen inches in height and nine 
inches in diameter ; to the centre of the bottom, where a perfora- 
tion had been made, was soldered the triblet tube, furnished with 
an ajutage, used in Experiment IIL, having two lateral holes, each 
e 
