[ 538 ] 
in larger quantities than from the fame water, when 
it is not moved by fuch mechanical agitation. 
This excellent invention of Dr. Hales may pro- 
bably be applied toother purpoles befides that, which 
he had principally in view, viz. the diddling of lea- 
water with greater eafe and expedition, with lefs 
fuel, and in fmaller veffels, than has hitherto been 
pra&ifed, for the benefit of navigators. 
It might be of lingular ufe, if it could be applied 
in the fire-engine. The great expence of large boilers 
in the conflru&ion of that machine, and the vail 
confumption of fuel in the working of it, render 
its ufes much lefs extenfive than they would be, could 
thofe expences be contracted. Various contrivances 
have with this view been tried ; and it is to be wifbed, 
that others could be dilcovered, that would more ef- 
fectually anfwer the end propofed. 
But air cannot be applied, in this engine, to in- 
creafe the quantity of the elaftic fleam, fince it would 
pais with the fleam from the boiler into the cylinder, 
and prevent a vacuum from being there produced, 
and hinder the pillon from moving therein. 
A mechanical agitation of the water in the boiler 
of the fire-engine may however be produced by 
other means fo as that a larger quantity of fleam may 
probably be raifed than can be effected in engines as 
commonly now conflruCted ; by which means the 
expences of conftruCting and working thofe ufeful 
machines may perhaps be greatly leffened. 
If, for example, the boiling water, inflead of be- 
ing agitated by air, as in Dr. Hales's method, was 
brifkly flirred about by a wheel placed in the boiler 
of the fire-engine ; it js probable, that by this means 
the 
