AOO Mr. de Luc on 
that thread is then Jhorter than it is moil times under the moijt 
vejfel. This M. de Saussure would have feen, if he had not 
been prevented, by the fituation of the index in his improved 
hygrometer , from trying again the effeCt of water on the hair ; 
and that phenomenon alone would furely have given a different 
courfe to his ideas ; efpecially he would not have fuppofed, that 
the hair lengthens 2 degrees more, by a fuper-faturation of the me- 
dium, or by the immediate contact of concrete water. 
-78. If, alfo, when he fettled the manner of determining 
the point of extreme moijlure on his hygrometers, M. de Saus- 
sure had retained the fimplicity of the procefs he had ufed for 
his fundamental experiments, in which a piece of wet cloth 
had been fufficient for producing the maximum of evaporation 
in his large veffel ; and, in confequence, had contented himfelf 
with inverting his glafs jar over water, without wetting it 
on the infide, he would have avoided a great caufe of decep- 
tion which I am going to explain. In my firft experiments on 
the comparative marches of our hygrometers, in which I fol- 
lowed M. de Saussure’ s prefcription for the moijl vejfel, I 
found fome anomalies which puzzled me. M. de Saussure 
himfelf took notice of them in the account I gave of thofe 
experiments, and attributed them to my inftrument. I did not 
agree with him in that refpeCt; but it was long before I could 
difcover the real caufe of thofe anomalies. The firft ftep 
towards that difcovery, was the reflecting on the ufelefliiefs of 
wetting the veffel on the inlide, for the only purpofe of pro- 
ducing in it the maximum of evaporation. That confideration 
engaged me to undertake a new courfe of the fame experi- 
ments, with a glafs jar merely inverted over water ; and by 
that means, the greateft part of the real anomalies being re- 
moved, I obferved clearly in the march of the hair, the 
combined 
