SILK-WORMS. 
135 
or hygrometers, or hygroscopes, all which terms 
mean measurers, or indicators of moisture. As it 
has been observed generally, that dry air is accom- 
panied by fine weather, the hygrometer is, there- 
fore, used in some places as a weather-glass. 
I shall not go farther into the peculiarities of 
these instruments, nor the materials with which 
they may be constructed; I will only say that they 
are very useful in the art of rearing silk-worms, 
and that they are to be had anywhere. By 
placing this instrument in the laboratory, it is 
most easy to see when the air is too damp, and 
to alter this by employing the remedies I have 
suggested for expelling the heavy air, and re- 
placing it by light fresh exterior air, which never 
can be so damp as the interior. 
It would be desirable to have two hygrometers 
in the laboratory, placed within a certain distance 
of each other, to ascertain the various degrees of 
moisture in different parts of the laboratory. 
There are hygrometers* joined with the ther- 
* I cannot sufficiently urge the use of these instruments to 
those who rear silk-worms, which indicates with such case 
one of the most powerful enemies of the silk-worm in the la- 
boratory. 
I trust I may not be imagined to recommend too many 
utensils or instruments ; I think I have mentioned only those 
that are indispensable ; without these instruments it would 
be impossible to distinguish in the laboratory", — 
1st. That the temperature is not only lower near the aper- 
tures, and higher near the stoves and fire-places, but also that 
