Theory of the Pneumatic Paradox. 301 



as the author of a new theory of storms, and one by Mr. Asa 

 Spencer. Another explanation, different in some respects from 

 either of the preceding, is contained in the number of the London 

 Mechanics' Magazine for June, 1839. 



Professor Espy's sokrtion of the phenomenon, is in some re- 

 spects similar to Mr. Abbot's, though, we if may judge from the 

 date of its publication, posterior in point of time. Being sup- 

 ported, however, exclusively by theoretical reasonings, it has left 

 the question still open to dispute, and the contradictory opinions, 

 which from time to time have since been advanced on the sub- 

 ject, would seem to show, that an attempt to detect their errors, 

 and to establish the true theory, on the basis of direct, unequivo- 

 cal experiment, would not be a work of supererogation. 



Prof Hare, whose explanation is similar, as it respects its lead- 

 ing principle, to that of Dr. Page, attributes the phenomenon to 

 the afflux of air against the disks, occasioned by the radiating 

 currents carrying with them, as they issue from between the 

 disks, some of the contiguous air. He demonstrates by a very 

 ingenious process of reasoning, that the velocity with which the 

 two disks tend, from the force of the blast, to move asunder, is as 

 many times less than the velocity of the blast, as the area of the 

 movable disk is greater than the area of the orifice of the tube. 

 Thus if the diameter of the disk and that of the orifice be as eight 

 to one, the area of the former must be sixty four times greater 

 than that of the latter, and consequently, in this case, the disks 

 have no tendency to move asunder with a velocity greater than 

 one sixty fourth of that of the blast. Hence he infers, that the 

 blast tends to communicate only a very small velocity, and inclines 

 with a very small force to separate the disks. It has been shown 

 that the afflux of air against the movable disk, though as the ex- 

 periment is usually performed auxiliary, is not essential to the 

 adhesion of the disks. It is however adequate to sustain the mere 

 weight of a second disk of letter paper, and of the same size of the 

 first, as may be thus shown. Through the centre of the movable 

 disk, to prevent it from sliding out of place, let a small needle pass 

 and project on each side. Having made a small hole through the 

 disk of letter paper, so that it move freely on the needle, place it 

 underneath the movable disk, and both underneath the fixed one. 

 On blowing through the tube, the disk of letter paper, being pro- 

 Vol. xxxix, No. 2.— July-September, 1840. 39 



