296 Theory of the Pneumatic Parador. 
Arr. Vi—An Attempt to determine by Experimental Research , 
the true Theory of the Pneumatic Paradox ; by Jos. Hate 
Axssort, of Boston, Mass. a 
In the year 1828, the following experiment, sometimes denom- 
inated the Pneumatic Paradox, was published in various journals 
in this country. “Cut a couple of cards each into a circle of 
about two inches in diameter ; perforate one of these in the cen- 
tre, and fix it on the top of a tube, saya common quill; make 
the other ever so little concave, and place it over the first, the 
orifice of the tube being thus under and almost in contact with 
the upper card. Try to blow off the upper card—you will find 
it impossible.”* To it was appended a statement, presumed to 
be apochryphal, that the Royal Society of London had offered a 
reward of one hundred guineas for a satisfactory explanation of 
it. Several have been published, both in this country and in 
England, but none that IT have seen seem to me admissible, either 
because the experiment may be so modified as wholly to set them 
aside, or because the principle on which they are founded may be 
demonstrated to be false. ; 
One explanation attributes the adhesion of the disks to the rare 
faction of the air, as it issues from the mouth, on account of its 
eee Pee 
* It is not material that the movable disk should be concave. The whole of 
wn over the mouth of the pipe, so that the strength of one man was 
to withdraw it. This experiment has often been shown to visitors 38 
sities of Manchester.” 
