310 Theory of the Pneumatic Parador. 
of tissue paper two inches long be held in the hand by one end, 
so that the other may rest against the hole, it will be blown away 
from it. ‘To obtain more exact results, I used a brass triblet tube 
similar to those already described, twelve and a half inches long, 
and three eighths of an inch in diameter, and having a lateral 
hole in the middle one line in diameter. The sectional area of 
the tube, therefore, was twenty and a quarter times greater than 
the area of the hole ; consequently, the latter would not, even 
on the supposition that the lateral and outward forces are equal, 
permit the issue of so much as one twentieth of the air expelled 
from the mouth ; notwithstanding which, the lamp was readily 
extinguished, and the strips of tissue paper repelled by the lateral 
jet of air. 
These results prove beyond the possibility of doubt, the fact of 
the lateral pressure of air forced through cylindrical tubes. It is 
not important to determine the comparative intensity of the on- 
ward and the lateral force ; the latter must be greater than the 
exterior atmospheric pressure, since the lateral jet could not other- 
wise take place. This fact being incompatible with the funda- 
mental principle by which Mr. Spencer explains the adhesion of 
the disks, his hypothesis necessarily falls to the ground. 
A writer in a late number of the London Mechanics’ Magazine; 
maintains, on the authority of an experiment of Mr. Tomlinson, 
that the movable disk is not retained in its place during the con- 
tinuance of the air-blast by exterior atmospheric pressure. As- 
suming also the principle which has just been disproved, that 
currents of air flowing through tubes exert no lateral pressure; 
and applying it to the currents that radiate from the common 
centre of the tube and disks, he asserts that “the disk is not re- 
moved because there is in fact no force to effect its removal.” 
He overlooks the tendency of the impulse of the blast to separate 
the disks, and leaves the adhesion of the movable disk against 
its own gravity, when it is placed underneath, unaccounted for; 
unless he means io be understood to refer it to what he calls “the 
attractive force of the air-blast,” when it is “spread out in a thin 
film” between the disks. The necessity of having recourse to 
_ 80 novel a supposition, will be obviated by the results I obtained 
eating the following experiment of Mr. Tomlinson. 
| brass tube, open at both ends, and terminated at the 
! screw, be fixed to the table of an air-pumpP- 
