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Intelligence and Miscellanies. 363 



Card, it will then be pressed forward by the atmosphere, 

 - Since the explanation depends entirely upon this 

 a^ principle it may be proper to prove it experimentally. 

 This may be done by tying a strip of paper to one ex- 

 tremity of the barrel of a quill, (A B) as represented 

 in the figure ; then by blowing tlu-ough the extremity 

 A although the paper may be bent from the onlice 

 y 8 if it is not without the influence of the wind, it will 

 be bent up beyond the direction of the element {a b) 

 of the quill and the extremity farthest from the orifice 

 / will be most elevated. In this case the wind removes 

 / a part of the pressure of the air, and it becomes ne- 



cessary that the paper should be inclined in a direction op- 

 posite to the wind, until the force of the wind exactly neu- 

 trahzes the pressure of the atmosphere on the opposite side, 

 and since the force of the wind diminishes, as the distance 

 increases, the paper should be elevated most, at the greatest 

 distance from the orifice, so as to compensate for the dimin- 

 ished force, by the increased inclination. Also if the paper 

 should be caused to make a greater angle with the direction 

 of the wind, on account of the increased pressure on the op- 

 posite side, it vvould be depressed to the former position. If 

 we now have a current of wind passing through 

 ^ the quill (A B,) when it meets the surface (C D) 

 it will have a tendency to pass oft" in a direction 

 parallel to that surface, and thus form a constant 

 current parallel to the card (C D,) and origina- 

 ting in the centre of the card. But the air will 

 y exert a pressure upon this current. To prevent this 

 ^ die card (H I) is placed near the extremity B, of 

 "" the quill, then since it is known (Nat. Phil.) tiiat 

 " if a body moves in a fluid at rest, a motion will be given to 

 the fluid in the direction which the body moves," the cur- 

 rent of wind which passes from the centre to the circumfer- 

 ence of the card in every direction will have a tendency to 

 draw out the natural atmosphere which may be between the 

 current and the card (H I,) the current will take the place 

 of that atmosphere, and the cards will approach each other 

 until the opposite pressures are equal, but if a force be ap- 

 plied to remove the card (C D) as it is removed, the space 

 between the cards being increased, the current of wind is 

 expanded, and that it cannot produce so great a pressure upon 

 the inner surface as before, (a part of the pressure from the 



