SILK-WORMS. 
137 
which is dried by this same blaze. I say blaze, 
and not fire, for two reasons : the first is, that, 
for instance, with two pounds of shavings, or of 
dry straw, there can be attracted from all points 
towards the chimney a large body of air, which 
issues at the flue of the chimney. While, in the 
meantime, this air is replaced by another quantity 
of exterior air, which spreads over the wicker 
hurdles, and revives the exhausted silk-worms. 
This change of air may take place without effect- 
ing any material variation in the degree of heat 
in the laboratory. If, on the contrary, thick 
wood were employed, it would require more time 
to move the interior air, ten times more fuel might 
be consumed, and the laboratory would be too 
much heated. The motion of air is, all circum- 
stances being equal, proportionate to the quantity of 
blaze of the substances that burn quickly. When 
wood-shavings or dry straw cannot be got, small 
sticks of dry and light wood may answer. As soon 
as the flame rises, the hygrometer shews that the 
air has become drier, and the degrees of it can be 
seen distinctly. 
The second motive which should lead us to pre- 
fer the blaze, is the light it diffuses. It cannot 
Well be imagined how beneficial this light is, which 
penetrates everywhere, nor how much it influen- 
ces the health and growth of the silk-worms. We 
ourselves often, when chilled by cold, or fatigued, 
