Hygrometry • 4 j 7 
which, comparatively to that of whalebone , have at firft finall 
fteps, and which confeoyiently move in an increafmg progref- 
fion, continue only to follow that progreffion ; and thofe which 
at firft have greatei -fteps, and confequently a decreafing march, 
have then final Ir fteps conformable to their individual law ; 
therefore, none of thole hygr of copes of both claiTes have any 
fudaen fart, produced by any degree of moifture in the medium 9 
or by the application of concrete water ; each of them fol- 
lows, from one end to the other of its fcale, itow n progreflion ; 
and in refpeft of flips, moifture is never extreme in the ambient. 
medium, as long as, in their refpeflive progreffions, they have not 
attained their great eft length . 
95. Our common hygrometer mu-ft then be made of one of 
the fhps\ but with that great diftimilarity obferved in their 
marches , which of them fhall we choofe as indicating the real 
march of moifture .? None as yet from that confideration.,, 
which I do not. even think a primary one. It is true, that if 
we truft to the increafes of weight in thole fubftances, as being; 
a means of afcertaining the real progrefs of moifture in the 
ambient medium , the mean rate of fix experiments of that kind 
related in this Paper, give the preference to the flip of whale- 
bone-, but this 1 do not yet con fide r as decifive, farther than in 
what relates to the comparative marches of flips and threads 
however, as my reafons of doubt on a more abfolute conclufion 
cannot be exprefled in a . tranfitory manner, I muft i ay them 
aftde for the prefent. 
96. But, as I have faid before, this is not what ought to 
determine our choice on the [ubftance of a common hygrometer , 
fince the obfervations themfelves are diftinft from the confe- 
quences to be drawn from them. Let us fuppofe the cafe 
(which I do not give up) that, with time and refearches, fome 
Vol. LXXXL I i i procefs 
