2^4. Mr. de Luc on 
68. Let us now fuppofe for a moment, that the above hygrofco - 
and the march that I attribute to the hair hygrometer, 
are real. In that cafe, if, during a conftant maximum of evapora- 
tion, the temperature varies from 32 0 to 8o°, moijlure will dimi- 
nish 4- and even l of the whole ; or, in other words, the ftate 
of the medium will be diftant by fo much from that in which a 
new introduction of vapour would be followed by a precipita- 
tion. But at the fame time, in the whole of that period of 
moijlure , the hair hygrometer is fuppofed to move only 1 or 2 
degrees backwards and forwards, with frequent irregularities. 
Therefore, in the hypothefis, fuch a great change of ?noiJlurc 
would be hardly fufpecled from thofe lmall deviations of the 
hair hygrometer, in which at firft nothing appears to be regu- 
lar ; and thereby it is evident, that, by confining himfelf to 
thofe experiments, M. de Saussure could not difcover thofe 
two important laws of hygrology and hygrometry , of which 
I have here only fuppofed the exigence. 
69. Let us fuppofe again, that the hair hygrometer had not 
exifted before a certain number of other experiments ; and that 
M. de Saussure, in his attempt to produce an inftrument of 
that kind, had fixed on any of the fiips made of fibrous vege- 
table or animal fubftances cut acrofs the fibres , of w T hich many 
hygtofcopes had been made before in a coarfer manner ; and 
that, in every other refpeft, he had proceeded as he has done 
with the hair. In that cafe, having placed his hygrometer and 
the manometer in the lame veflel, with a quantity of water 
iufficient for producing the maximum of evaporation in every 
common temperature , and obferved alfo the points where 
both iaftrumeiits flopped in different lafting temperatures , he 
then would have found ; that the hygrometer indicated lefs and 
lefs moijlure 9 at the fame time that the manometer , by afcending 
more 
