s 
318 Theory of the Pneumatic Paradoz. : 
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. Lovering, 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, be relinquished it, engaged 10 # 
course of nice experiments to ascertain the practicability of ad- 
Vantageously making starch on a large scale from the potato, 4™ 
invented the machinery and processes by which that article 35 
‘how manufactured in the Northern States, to the annual amount 
of probably five or six million pounds. He thus originated 
