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XCV1I. An Attempt to improve the Marnier 
of working the V entilators by the Help of 
the Fire-Engine. In a Fetter to Tho. 
Birch, D. D Secret . R. S from Keane 
Fitz-Gerald, Efq\ F. R. S. 
S I R, 
Read June 8, / | A H E reverend and ingenious Dr, 
Hales, from whom mankind has 
received fuch benefit by his ufeful application of 
ventilators, being inclined to extend its ufe to thofe, 
who work in mines at great depths under ground, 
where the lives of many are loft by damps and noxi- 
ous vapours, occafioned by the want of a free cir- 
culation of air ; and finding by experience, that ven- 
tilators worked by wind do not operate above one 
third part of the year, and in calm hot weather, 
when moft wanted, do not operate at all ; did me 
the honour of applying to me for affiftance in con- 
triving a machine to work the ventilator, by the help 
of the fire-engine, which is now generally ufed in all 
mines for drawing off the water ; and which I have 
accordingly attempted, and hope it will anfwer the 
purpofe. 
As the lever of the fire-engine works up and down 
alternately, and performs at a common medium about 
a dozen ftrokes in a minute, it was neceffary to con- 
trive fome way to make the beam, tho’ moving al- 
ternately, to turn a wheel conftantly round one way, 
and alfo to increafe the number of ftrokes to fifty or 
fixty in a minute. 
Th e 
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