m ees qu. Li dp rie y; 
RXV Zu Account of en inte — 1 
with: Jome Obfrvations on thè common OE ‘and Mr. 
-SMEA TON’ improvement + qua Letter from the R ev. JOHN: 
j Prince fo the Rev. Josep WILLARD, Print f th 
p Univer f Cambridge. Mei. 
n Salem, Now! 10, 184: ^ 
a5] REV. AND DEAR: SIR; pa 27 Shorts ARAR MUS HONS 
Å GREEABLE toyour requeft, Iwill endeavour to give 
HA you fome account of the air-pump T have lately- ‘con 
firudted, upon a plan different from any I have ever feen: ^: 
i? Reading the account of the ingenious Mr. \Smeaton’s air. 
pump, in vol. xlvii. of the Philofophical "Tranfations, and 
the high recommendation of it by Dr. Prizfiley, in vol: lxiv. of 
d fame work, I was defirous of poffeffing oné ‘of that kind + 
| > by the Doétor's paper, they were not comiionly 
made:by the philofophical i t:makers in Londoh, it ink 
duced nie to ‘attempt making Bos AURME »- er 
as Icould get here. |^ ^ 
«Before I had proceeded far, I Pe Mr. ‘Smeaton’ + pump 
olikin Anand; ifnof in its power -of rarifying the air, at 
left in- ifmbligi ái HW Abi iaie d die: Gai idis 
Pu ia ossi $2. 
to confider whe dacióale: of an air-pünip; pend eet fome "vet 
vations on. Mr. 'Smeaton' s. It is well küowh that the valve at 
the bottom of the barrel of an'air- pump is opened by the fpring 
of thear a&ing againft it'underneath, when the weight of the 
air is removed’ from thé top of the valve, by raifing the pifton 
in-tlié bar£el.:|-In order toremove this refiftance from the top 
of the valve moft effe&uálly; the pifton fhould be made to fit 
very exactly :to.. the- wale! pite; tien put down upon it: 
for if there be any fpace between, the bottom of the pifton and 
Ppp valve, 
# 
