138 
THE ART OF REARING 
or exhausted, feel revived by the cheerful light of 
a bright fire, whilst the mere heat of the fire, 
without the blaze, never produces this effect. 
We must then conclude that the fire of large 
wood, or of the stove, is always useful when it is 
required to maintain a steady temperature in 
a laboratory, and that the air of it is not very 
damp ; but that when we want to renew the air, 
charged with too much humidity, and replace it 
quickly with exterior air, we should use the blaze. 
When I particularly describe the laboratory, I 
shall enlarge on this subject. (Chap. XIII.) 
Hitherto I have spoken of the humidity disen- 
gaged from the air of the laboratory, of which I 
shall give a calculation (Chap. VIII. § 7.); but I 
have not yet mentioned the moisture with which 
the external atmosphere often is loaded. 
A barometer, placed in a contiguous room, or 
outside, will shew the state of the atmosphere. 
Should it be damp it would increase the dampness 
of the laboratory, and this should be rectified by 
frequently-burning blazes in the fire-place, to mak e 
the air more pure and drier than the exterior at- 
mosphere. Small fires should also be often light- 
ed, not to communicate great motion to the exte- 
rior atmosphere, but only to keep up a gentle and 
gradual agitation in the interior air, which is most 
beneficial to the silk-worm. In keeping up a gentle 
and constant motion of the air, the ■worms derive 
