S60 Mr Anderson’s Corrections for the Effects of Humidity 
most accurate comparisons of them which have been made. By 
the results furnished by De Luc himself, of his hygrome- 
ter answers to 73° of Saussure ; whereas, according to the ob- 
servations of Du Long, 31° -8 answers to 75°, and 37°’5 to 84 ; 
which would make 35° to correspond with 80°. Some allowance 
must be made for the aberrations of different instruments ; but 
if we adopt the mean of these results, 35° of De Luc’s should 
correspond with 76*5° of Saussure’s, which, according to the 
elegant analytical investigation of Biot, founded on the experi- 
ments of Guy Lussac answers to *5599 as the tension of va- 
pour. This differs *016 from the result furnished by my for- 
mula, a difference so small as to be within the limits of the de- 
viations of different instruments. 
( To he continued. ) 
Art. VIT. — On the Prhiciples and Practice of Ventilating and 
Wai'ming Buildings. By Thomas Tiiedgold, Esq. Civil 
Engineer, and Honorary Member of the Institution of Civil 
Engineers. (Concluded from p. 47.) 
Of W arming Buildings. 
The principles of warming buildings depend on the laws by 
which hot bodies communicate heat, limited by the circumstance 
that the air which is to be respired, must not be injured by the 
heating surface. And it is obvious, that the quantity of heat 
required, must depend very much on the closeness of the win- 
dows and doors, the kind of walls, and the proportion of win- 
dows. The effect of different kinds of walls will be most sen- 
sible in the time necessary to raise the room to its proper tem- 
perature, but the escape of heat from doors and windows will 
be constantly taking place. It may be shown, that each foot of 
surface of glass will cool about IJ cubic feet of air per minute, 
from the temperature of the room to that of the external air ; 
and hence the loss of heat from windows is easily estimated. 
To the loss of heat from the windows, must be added the quan- 
Physique, tom. ii. p. 199. 
