312 Theory of the Pneumatic Parador. 
sage and barrel, and then in a full gush into the receiver through 
the tube, when a disk of card three inches in diameter was imme- 
diately blown off. I repeated the experiment with a very excel- 
lent air-pump, made by Mr. Joseph Wightman of this city, capa- 
ble of producing the degree of exhaustion just described, and hav- 
ing a passage for admitting air into the receiver one fifth of an 
inch in diameter. ‘The tube to which the perforated disk was 
adapted being of the same diameter with the air passage, and the 
latter being closed with the thumb, and the air exhausted to the 
one two hundred and fortieth part, on suddenly removing the 
thumb a circular card three inches in diameter, and on another 
trial, a disk of tinned sheet iron two inches in diameter and 
weighing forty nine and a quarter grains, were blown nearly to 
the top of the receiver. By reducing the size of the disk, a less 
degree of exhaustion becomes necessary in order to blow it off. 
If it does not exceed one inch in diameter, it is not necessary to 
exhaust the air to more than a sixtieth part, though I have found 
it impossible, when the apparatus is adapted to the stop-cock of a 
condensing chamber, the tube being one eighth of an inch in di- 
ameter, to blow off a movable disk one inch in diameter by 
means of a very powerful current of highly condensed air. 
Having completed the ungrateful labor of pointing out the 
errors of ‘the various theories that have been proposed to explain 
the pneumatic paradox—which seem- Fig. 6. 
ed however a prerequisite to the undis- 
puted admission of the correct one— 
I now proceed to adduce the proofs of 
the theory contained in the first part 
of this article. 
Experiment I. In order to show that 
rarefaction may be produced in a space 
having a free communication with the 
external air, I cite the following. expe- 
riment of Hauksbee. 
In two opposite sides of a small box 
holes were made, one somewhat larger 
than the other, and to these holes were 
adapted the short tubes A and B, seen : fe 
in the accor npa ying figure. ‘Through the top passed in an alt 
tight manner a barometer tube, the lower end being immersed 
