for adjujUng Thermometers, 851 
the chimney with the tin plate ; and there is lefs need to 
make the cover fit clofe, only it mnft be obferved, that 
the clofer the cover fits, the lefs the operator will be in- 
commoded by the fleam. The height of the barometer 
at which the boiling point fhould be adjufted, when this 
method is ufed, is 29^- inches, or three-tenths of an inch 
lefs than when the former method is nfed. 
It will be convenient to have two or three pots of dif- 
ferent depths; for if a fliort thermometer is to be ad- 
jufted in the fame pot which is ufed for a long one, it 
will require a great depth of water, which, befides taking 
up more time before it boils, makes the obfervation 
rather lefs accurate, as the heat feems to be lefs regular 
when the depth of water in the pot is very great, than 
when it is lefs. 
Perhaps fome perfons, for the fake of heating the 
water more expeditioufly, may be inclined to ufe-an ap- 
paratus of fuch kind that the fire fhall be applied to a 
confiderable part of the fides of the pot as well as to the 
bottom; we would, however, caution them againft any 
thing of that kind, as the obfervations are confiderably 
lefs regular than when little more than the bottom of 
the pot is heated. If the pot is heated over a chafing-difh 
or common fire, we apprehend that there can feldom 
be any danger of too much of the fides being heated; 
5 O 2 ' bu 
ft 
