826 Report of the Committee 
If this cover to the chimney had been heavy, the in- 
cluded fleam might have been fo much compreffed 
thereby, that the water and ftearn might have acquired a 
coniiderably greater heat than they ought to have done; 
but as this plate lay loofe on the chimney, and as its 
weight was not greater than that of a column of quick - 
fdver, whofe bafe is equal to that of the mouth of the 
chimney, and whofe altitude is ^-th of an inch, the excefs 
of thecompreffionof the included ftearn above that which 
it would fuffer in an open veffel, could not be greater 
than that which would be caufed by an increafe of ~th 
of an inch in the height of the barometer, which is too 
fmall to be worth taking notice of; for, if the excefs of 
compreffion was greater than that, the tin plate mult 
necefTarily be lifted up fo much as to afford a fufficient 
paffage for the fleam to efcape faft enough, though 
urged by no greater force than that. 
Though in the different trials of the fame thermo- 
meter in fleam, on the fame day, and with the fame 
water, fo little difference was obferved, according to the 
different manner of trying the experiment; yet there 
was a very fenfible difference between the trials made on 
different days, even when reduced to the fame height of 
the barometer, though the obfervations were always 
made either with rain or diftilled water. The difference, 
4. however. 
