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XXIII. Defcription of an improved Air-Pump , and the Account 
of Jome Experiments made with it . By Mr. Tiberius Cavallo, 
F. R. S. 
Read July 3, 1783. 
T HE principal improvements which the air-pump received 
fmceit was fi rid invented, were contrived by Mr. smea- 
ton, f. r. s. and are deferibed in theXLVIIth volume of the 
Philofophical Tranfaftions. This ingenious gentleman, conli- 
dering the imperfedtions of the air-pumps ufually made, not 
only found means to correct feveral of them, but improved 
almoft every part of the machine, lb as to render it incompara- 
bly fuperior to any thing of the kind done before. 
It appears, by fome accurate experiments of Mr. nairne, 
e. r. s. deferibed in the LXVIIth volume of the Phil. Tranf* 
which were made with an air-pump conftrudted after Mr. 
smeaton’s principle, that by means of the belt air-pumps 
made before Mr. smeaton’s invention, the rarefaction of the 
air within the receiver could never have been brought to more 
than forty or fifty times, if the heat of the place was about 
57 0 ; that even with Mr. smeaton’s pump the receiver could 
not be exhaufted beyond 70° or 8o° of rarefaction, when moift 
leathers were ufed, or moifture was in any way introduced 
within the receiver ; but that when this pump is quite free 
from moifture, and is newly cleaned, oiled, and put together,, 
then 
