[ 21 7 ] 
EXPLANATION OF THE INSTRUMENTS. 
The inftruments with which the foregoing obfervations were 
made are the fame that were ufed in former obfervations of 
this kind, a full account of which was given by Henry 
Cavendish, Efq. F. R. S. in the LXVJth Volume of the 
Philofophical Tranfadti'ons ; but as they have been moved from 
the fituations they had at that time, it may not be amifs to men- 
tion how they are placed now, in order the better to fhew 
what degree of accuracy may be expected from them. There 
being no one lltuation for a thermometer out of doors fo good 
as could be wilhed, it became necefifary to make ufe of 
two thermometers ; each is placed out of a three-pair of- 
ftairs window, one facing E.N.E. and the other W.S.W. 
and they ftand about two or three inches from the wall, 
that they may be the more expofed to the air, and the lefs 
affefted by the heat and cold of the houfe. As the fun fhines 
on theeaftern part of the building in the morning, the thermo- 
meter to the wefhvard is made life of for the morning obfer- 
vation during that feafon of the year when the fun rifes high 
enough to affedt the other ; for all other obfervations, that to 
the eaftward is employed. Neither the building oppofite, nor 
that on the fouth fide of the thermometer to the eafi:, are 
elevated above it in an angle of more than if ; but the oppofite 
building is not more than twenty- five feet diftant. The 
thermometer to the weftward will not be aftedfed by any othei 
building than one to the northward, which is elevated above 
it in an angle of 20°, and which is only twenty feet diftant. 
Vol. LXXVIII. F f The 
