42 
THE ART OF REARING 
low priced as they are, are imperfect; the tube in 
general is of an unequal interior diameter, which 
may lead into errors. The expense should not be 
considered, as good thermometers, made with 
quicksilver, are of the utmost consequence*. 
It sometimes occurs, that the tube of the ther- 
mometer is loose, and is misplaced on the scale ; 
this may occasion errors. To remedy this incon- 
venience, several thermometers should be placed 
horizontally near each other on a table, upon 
which should be similarly placed a correct thermo- 
meter ; they should be left thus one hour, to ascer- 
tain their precise indications, and then the tubes 
may be either raised or depressed, and regulated 
by the correct thermometer, and then fixed with a 
little melted sealing-wax. 
Some persons imagine that they can judge of 
* Besides the thermometer, there is another valuable in- 
strument for the cultivator of silk-worms, the thermometro- 
graphe, invented by M. Cluson Bellani de Monza. This in- 
strument indicates the different extremes which have occurred 
in the temperature in a particular space of time. With this 
instrument, the cultivator may know, every morning, always 
the variations which the temperature has undergone in the 
hot-house ; and may thus watch whether he, whom he has 
trusted with the management of the stove, has done his duty 
with exactness. The degrees of heat experienced in the hot- 
house may thus he equally known in a certain time. It Is 
• needless to state any further the important use of this instru- 
ment. It is a public benefit when enlightened men apply the 
principles of abstruse science to the useful arts. 
