3"58 Tropofalfor a new tJjgroihettr. 



it as a "perfect and complete inftrument. I wifli merely t$ 

 communicate my ideas on the fubje<5t, and to give others air 

 opportunity of examining it farther, and of perhaps pro- 

 ducing fomething that may be better calculated to anfwer the 

 intended purpofe. It ts, indeed, much to be wilhed, that an 

 accurate hygrometer could be invented ; as it maybe readily 

 conceived that fuch an inftrument would be of the utmoft uti- 

 lity, not only to naturaliits, but alio to farmers and others. 



The molt common hygrometer, known under the name ol 

 a weather-houfe, is founded on the property of feveral twilled 

 fubftances to untwi-ft themfelves in a moill atmofphere, and 

 then to twift themfelves back when the weather is dry. The 

 fubftances chiefly employed are cat-gut ; and, when required 

 ona large ical.e, hempen ropes. Caifcbois, aBenedictinc monk, 

 at Metz, propofed another hygrome^c, whteh conlifts of the" 

 gut of a (ilk-worm. When that infect is ready to fpin, there 

 are found in it two veflele proceeding from the head to th* 

 ftomach, to which thev adhere, and then bend towards the 

 back, where they form a great many folds. The part of thefe 

 vefl'els next the ftomach is of a cylmdric form, and about a 

 line in diameter. Thefe veflels contairl a gummy fort of 

 matter from which the -worm fyins it? filk ; and, (hough 

 they arc exceedingly tender, means have been devifed to ex* 

 trael them from the infect, and to prepare them for the above 

 purpofe. When the worm is about to fpin, it is thrown in- 

 fo vinegar, and rufteretl to remain there twenty-four hoiirrf; 

 during which time the vinegar is abforbed into the body of 

 the infect, and coagulates itg juices. The worm bung then 

 opened, both the vefTets, which have new acquired ftrength, 

 are extracted; and, on account of their pliability, arc ca- 

 pable of confide rahle extension. That they may not, how- 

 ever, become too weak, the) are ftretched only to the length 

 of about fifteen or twenty inches. It is obvious that they 

 mult be kept hiffieiently extended till they are completely 

 dry. Before they attain to that ftate they muft be freed, by 

 means of the nail of the finger, from a flimy fubftance which 



adhere- 



