Hygrdmetry . 397 
tried that method for fixing their point of extreme moijhtre, as I 
had done for my firft hygrometers. But in thofe trials he obferved, 
that while his inftruments flood in water, their indications re- 
mained undetermined within a fpace of four or five degrees ; and 
attributing that irregularity to a friShon of the hair with water , 
he thought it neceflary to change my method, to that of placing 
the injirument in a moijl medium, which he produced by means 
of a glafs jar, wet on the infide, and inverted over water. In 
this method, the fituation of the index became indifferent ; 
and, for fome particular reafon, he placed it at the bottom or 
his new hygrometers, which then could not be plunged into 
water. This laft circumftance was merely accidental ; how- 
ever, we fliall fee how much it has influenced his opinions 
in refpect of extreme moijhtre. 
In the firft account of his experiments, M. de Saus- 
sure did not enter into thofe particulars ; but they are in his 
anfwer to me : and when 1 there faw, that he gave as a reafon 
for having abandoned the immerfion in water, that a Jirong ad- 
hefion of the hair to that liquid impeded the freenefs of its 
motions, I found it more natural to affign to the inftrument 
itfelf the unfteadinefs of its index which he attributed to that 
caufe. Indeed, in thofe firft hygrometers, one end of the axis 
paffed through a hole for the purpofe of carrying the index out- 
wards, which was a caufe of much fridion : that axis befides 
was loaded with the weight of pretty large pincers, holding 
the hair, and that weight was counterpoifed on the other fide. 
Laftly, the connexion of the hair with the index was produced 
by a filver lamina, which, though very thin, oppofed fome re- 
fiftance in bending round the axis. Thofe are defe&s that M. 
DE Saussure correded afterwards; but they exifted in the 
inftruments which he plunged into water , and a weight or 
