IV. On the Pressure produced on a flat Plate when 

 opposed to a Stream of Air issuing from an Orifce 

 in a plane Surface. 



By ROBERT WILLIS, B.A. 



FELLOW OF CAIUS COLLEGE, AND OF THE CAMBRIOOE PHILOSOPHICAL SOCIETY. 

 [Read April 21, 1828.] 



The singular and apparently paradoxical result obtained by 

 opposing a flat plate to a current of elastic fluid issuing from an 

 orifice in a plane surface, has lately excited considerable interest, 

 especially on the Continent, where it was first brought into notice. 

 In its simplest form the experiment consists in this. If we blow 

 through a tube, the aperture of which terminates in a flat plate, 

 and apply a circular disc of card or any other convenient ma- 

 terial to the aperture, we find that as long as the blast is continued, 

 the disc is attracted to the plate instead of being repelled, as might 

 naturally have been expected. Some pins must be fixed into the 

 plate, to prevent the disc from slipping off sideways. 



This appears to have been first discovered, apparently by 

 accident, at the iron-works of Fourchambault, where one of their 

 forge-bellows opened in a flat wall, and it was found that a board 

 presented to the blast was sucked up against the wall. It was there 

 exhibited to Messrs. Thenard and Clement Desormes, in October 

 1826, and shortly afterwards a paper appeared in the Bulletin 

 Universel, in which the latter gentleman considered a similar 



Vol. III. Part I. R 



