Intelligence, fyc. 395 



2. Plane surfaces not separated by a blast in certain cases. 



Wallingford, Vt. May 16, 1828. 

 TOP ROF. SILLIMAN. 



Dear Sir — I beg leave to call your attention to a fact, 

 for the explanation of which a gold medal and one hundred 

 guineas were offered by the Royal Society. 



The experiment is this ; cut from a card two pieces about 

 two inches in diameter, let one of them be perforated in 

 the centre, and let a common quill be introduced into the 

 perforation, with one end even with the surface of the card 

 — let the other piece of card be made a little convex, and 

 lay its centre over the end of the quill, with the concave 

 side of the card down — the centre of the upper card should 

 be from { to i of an inch above the end of the quill. On 

 attempting to blow off the upper card, by blowing through 

 the quill it will be found impossible. 



I prepared the pieces of card very carefully, according to 

 direction, and to my astonishment, the upper card could 

 not be blown off. 



When the edges of the two pieces of card were made to 

 fit each other very accurately, the upper card would be 

 moved, and sometimes it would be thrown off, but when 

 the edges of the card, were on two sides, sufficiently far 

 apart to permit the current of air to escape, the loose card 

 retained its position, when the current of air sent against it 

 was strong, when it was inclined at every angle through 

 180° ; but when very little inclined, if the current of air 

 ceased, the upper card would immediately fall. The exper- 

 iment succeeds equally well, whether the current of air be 

 made by the mouth, or from a bellows. When the tube fit- 

 ted the perforation of the card rather loosely, a comparative- 

 ly light puff of air would throw both cards three or four feet 

 in height. When, from the humidity of the breath, the up- 

 per surface of the perforated card had a little expanded, 

 and the two opposite sides were somewhat depressed, these 

 depressed sides were distinctly seen to rise and approach 

 the upper card directly in proportion to the force of the cur- 

 rent of air. 



I have this moment discovered another fact with this sim- 

 ple apparatus, equally inexplicable with the former. Let 

 the loose card be laid upon the hand with the concave side 

 up — blow forcibly through the tube, and at the same time 



