SILK-WORMS. 
41 
2. The necessity of determining by the Thermo- 
meter, the suitable degree of heat for hatching 
and rearing the Silk-worm. 
To produce, maintain, and regulate the degree of 
heat necessary in the space allotted to the hatching 
and progress of the silk-worrn, we must imitate 
the botanist in the management of the hot-house, 
and employ the thermometer. By this valuable 
instrument, we clearly see that it is of less im- 
portance that the silk-worm should live in a tem- 
perature equal to the heat of its native climes, 
than that it should be preserved from violent 
transitions, and thus it should be reared in an 
even and progressive temperature. 
The thermometer (Fig. 4), simple in itself, as it 
cannot be affected by the caprice and will of man, is 
a certain method of attaining this important object 
of an even temperature ; and although it is not the 
only requisite instrument in this art, as I shall shew 
in Chap. VII., I at present shall mention it alone. 
We shall require several well-constructed ther- 
mometers. 
Thermometers are either made with quicksilver 
or spirits of wine. Those made with quicksilver 
are always the most desirable, because the expan- 
sion and condensation of that metal are more ex- 
act than those of the spirits of wine. Besides the 
thermometers manufactured with spirits of wine. 
