Theory of the Pneumatic Parador. 309 
tube. This proposition is subject to one or two limitations, 
When, in Experiments III and IV, the water in the reservoir was 
allowed to discharge itself to the level of the tube, it ceased to 
escape in the form of a jet, though not to drop from the lateral 
holes, after its head was reduced to a few inches, and in the case 
of tubes not having an ajutage, after it was reduced to a little 
more than a foot. Also, if descending tubes of considerable 
length be employed, there will be no lateral jet beyond a certain 
depth, since in obedience to the laws of falling bodies, the de- 
scent of the water will be constantly accelerated by gravity ; and 
this effect will finally become such as to overcome the mutual 
adhesion of the particles, and the lower portions becoming detach- 
ed from those above, will leave void spaces, into which, if lateral 
holes be made, the surrounding air will rush, and be carried down 
with the stream. 
I have described the foregoing experiments with considerable 
minuteness, on account of the importance they possess, inde- 
pendently of their connexion with the main object of the pre- 
sent article, as proofs of a controverted if not new principle of 
hydraulics. They do not prove that the lateral pressure of water 
flowing through cylindrical tubes is equal to that of water in a 
State of rest under the same head. It is undoubtedly less, but to 
determine in what precise degree it is less, would be an exceed- 
ingly difficult problem, the solution of which is not necessary to 
my present purpose. 
It remains to be shown that Mr. Spencer’s proposition is false, 
as it respects aeriform fluids as well as liquids. The experiments 
with the tubes of tissue paper, described in the first part of this 
article, prove not only that air in a state of motion is not, asa 
necessary consequence, in a rarer state than the ssinislitings at- 
mosphere, but that, when it is blown through tubes of a uniform 
bore, and having orifices equal to that bore, it exerts a lateral pres- 
sure. The following additional experiments corroborate the same 
conclusion. 
Exp. I. Make with care several holes of various sizes, from a 
twentieth to an eighth of an inch in diameter, and at intervals of 
an inch or two, in a brass tube one eighth of an inch in diameter ; 
on blowing strongly through it, the air will issue in an oblique di- 
rection from either hole, when the others are stopped, with such 
force as to extinguish a common lamp. _—! if a narrow strip 
Vol. xxxix, No. 2.—July-September, 1840. 
