[ 154 ] 
fuddenly throwing in too great a quantity of cold air, 
when the pores are opened by fo great a degree of 
heat, has probably hindered the application of venti- 
lators to this purpofe. But, by this means, all dan- 
ger on that account would be avoided with certainty, 
as the bars could be adjufted to any two degrees of 
heat, within which, there could be no danger. 
I have ventured thus far on fpeculation, as I can have 
no doubt of the power of metals by expaniion ; and 
imagine it will readily be allowed, that a ventilator 
may be worked by a weight, as well as by wind. 
I fend your Lordfliip a drawing of the barometer 
and thermometer, and have placed the inftruments 
for the infpe&ion of the gentlemen of the Royal So- 
ciety, in their meeting-room ; where, if agreeable, I 
lhall leave them for fome time. 
There have been fome very ingenious methods 
contrived, to mark the variations that happen during 
the abfence of the obferver ; but I do not know, that 
any attempt has been made in this manner. I wifh 
thefc regifters may be found to anfwer the purpofe ; 
and am, with great refpedt, 
My Lord, 
Poland-Street, 
May 6, 1761. 
Your Lordfhip’s mod obedient- 
humble fervant, 
Keane Fitzgerald. 
XXX. An 
