Theory of the Pneumatic Paradox. 315 



Experiment Y. Let the compound tube just described, having 

 its cyhndrical part one eighth of an inch in diameter, be adapted 

 to a stop-cock screwed into a ground brass plate, and pass down 

 from it into a very large open mouthed receiver. On exhausting 

 the air to the one three hundredth part, and suddenly opening 

 the stop-cock to readmit the air, a narrow strip of tissue paper, 

 attached by the upper end, so as to have its lower end press against 

 a hole in the smaller part of the diverging tube, will be blown 

 from the hole. This experiment, in connection with the fact 

 that on hlotoing through the tube, air is drawn into the same 

 hole, proves that the direction, whether inward or outward, of 

 the air that passes through lateral holes made in tubes through 

 which air is forced, depends upon the comparative density of the 

 internal and external air. 



Experiment VI. Instead of the fixed disk, substitute a plate of 

 tinned sheet iron about one foot square, perforated in the middle, 

 and having a tube one quarter of an inch in diameter soldered at 

 the same place. Drill holes in the plate one line in diameter, at 

 various distances around the orifice, the nearest bordering on the 

 tube itself. Having closed all but one of the holes by means of 

 small pieces of tissue paper and gum arable, support the plate in 

 a horizontal position, and apply underneath a plane disk of tinned 

 sheet iron, two inches in diameter, and having a cambric needle 

 slightly projecting from its centre into the tube to keep it in place. 

 On blowing through the tube with sufficient force to make the 

 disk adhere, it may be ascertained whether air is drawn inwards 

 or issues outwards through the open hole, by laying, after the 

 blast has commenced, (at the instant it commences, for obvious 

 reasons, there is a little puff of air outwards, ) a piece of tissue 

 paper upon the hole large enough to cover it, and having a narrow 

 filament extending from one side for the convenience of holding 

 it by a pair of forceps. Proceeding in this manner, I found the 

 air drawn in at all the holes, including the one bordering on the 

 tube itself, whose distance from the orifice did not exceed three 

 quarters of an inch. At all the holes nearer the circumference of 

 the disk, the air issued outwards. With a similar disk three 

 inches in diameter, the air was found to be drawn in only to the 

 distance of a little more than half an inch from the tube, beyond 

 which it issued outwards. In this experiment a disk of card is 

 objectionable on account of its soon becoming moist and warped. 



