[ 207 ] 
dex refpeding the point of o, this movement is 
only to be confidered as a rough or preparatory ad- 
juftment, to bring it within the coinpafs ol the 
Hide of the fcale ; which will not often happen 
to be neceffary after the fiift time j but in this cafe, 
the adjuflment muft be repeated in the fame man- 
ner, by drying and wetting as before defcribed. 
It is to be remarked, that, as the cord is fuppofed' 
impregated in a given degree with common fait,, 
and this not liable to evaporate, care muft be 
taken in wetting, that no drops of wet be luffered 
to fall from the cord : for, by the obfervance hereof,, 
the original quantity is preferved in the cord. 
Obfervations ,mad€ upon two original Hygrometers. 
Thefe hygrometers were firfl adjuded, after the- 
impregnation of the cords with common fait, in 
February 1770 ; they were kept together in a flair- 
cafe till the fummer following ; they were frequently 
obferved, and rarely found to differ more than one 
degree. 
In fummer, one of them remaining in the former 
place, the other was removed into a paffage through 
a building; which having no doors, and the inftru- ' 
ment being hung fo that neither rain nor the diredl 
rays of the fun could fall upon it, thereby it became 
expofed to the winds, and the free paffage of the 
open air. In thefe fituations the two hygrometers 
not only differed very greatly in quantity, but even 
frequently were moving different ways. They were 
thus continued till January 1771J in which fpace of 
time I obferved, that the moft ordinary place of the 
, index. 
