Theory of the Pneumatic Paradoz. 315 
Experiment V. Let the compound tube just described, having 
its cylindrical part one eighth of an inch in diameter, be Adapted 
to a stop-cock serewed into a ground brass plate, and pass dow 
from it into a very large open mouthed receiver. On exhavitiies 
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 blowing 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 arabic, 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 air outwards, ) a piece of tissue 
paper upon the hole large enough to cover it, and- having a harrow 
filament extending from one side for the convenience of holdi 
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 aninch. 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, 
