318 Theory of the Pneumatic Paradox. 



nearly stationary air ; and the elasticity of the interposed air, 

 greatly diminished by the rarefaction around the tube. On the 

 other hand, the disk is urged upwards by the atmospheric pres- 

 sure underneath, assisted, though not essentially, by the currents 

 striking against its under surface ; the latter forces preponderate, 

 and the disk adheres. 



The following modification of the experiment of the pneu- 

 matic paradox admits of easy explanation, in conformity with the 

 principles established in this article. Condense the air strongly 

 into a condensing chamber partly filled with water, and adjust 

 the tube, with the perforated disk attached, to the stop-cock. On 

 applying the movable disk and opening the stop-cock, the water 

 is forced against the movable disk, which adheres in the same 

 manner as when air is used. In this case the water, which, not 

 being expansible, may be seen not to fill the whole space between 

 the disks, carries with it a portion of the interposed air, and the 

 rarefaction thence resulting causes the adhesion of the disks. 



Most of the original experiments I have described, have been 

 repeated with George B. Emerson, Esq. of this city, President of 

 the Boston Society of Natural History ; those which required an 

 air-pump were performed with Prof. Levering, by whose kindness 

 I was permitted to make use of the very powerful instrument be- 

 longing to his department in Harvard University ; and several of 

 those undertaken to determine the truth of the proposition advan- 

 ced by Bossut, were repeated with Professor Treadwell, likewise 

 of Harvard University, to whom I am indebted for several valua- 

 ble suggestions. 



I feel unwilling to bring this article to a close without adding 

 a brief tribute to the memory of the late lamented Samuel Ab- 

 bot, Esq., the gentleman whose theory of the pneumatic paradox 

 I have attempted to establish on the basis of experiment. Hav- 

 ing been bred to the bar, he practiced his profession several years 

 in New Hampshire, and subsequently in Massachusetts, with the 

 reputation of being an accurate and able lawyer. Not finding it 

 however congenial to his tastes, he relinquished it, engaged in a 

 course of nice experiments to ascertain the practicability of ad- 

 vantageously making starch on a large scale from the potato, and 

 invented the machinery and processes by which that article is 

 now manufactured in the Northern Slates, to the annual amount 

 of probably five or six million pounds. He thus originated a. 



