20 
Mr. De Luc on 
grology , of which however I (hall only give here the general 
and conftant refults, as furnilhed by thofe hygrofcopes. 44 The 
44 maximum of evaporation in a mafs of inclofed air is far from 
46 being identical with the maximum of moijiure ; this being 
44 dependent alfo, even to a very great degree, on the tempera - 
46 ture of the fpace y fuppofed to be the fame, or nearly fo, as that 
44 of the water which evaporates in it. Moijiure may arrive to 
44 its extreme in an inclofed air y if that common temperature 
44 is near freezing point % but it becomes lefs and lefs, even to a 
44 very dry ftate, as that temperature rifes, though the produtl 
44 of evaporation , thereby increafing, continues to be at its dif- 
44 ferent maxima , correfpondent to the different temperatures ” 
This is a very important propofition in hygrology ; which, from 
my experiments, would not be fubjefl: to any obje&ion, if there 
were no other hygrofcopes than thofe I haye mentioned above, of 
which I have thirteen different fpecies ; but there is another 
clafs of fuch inftruments, from which fome doubt might firft 
arife ; and I come now to that point. 
On two dijlinB claffes of hygrofcopes. 
3 1 . As I fhall now frequently fpeak of flips and threads , 
which conflitute thofe two clajfes of hygrofcopes , I muft firfh 
explain what I mean by thofe words. The flips compofe the 
clafs of hygrofcopes ufed in the above experiments ; they confifl 
of very thin and narrow laminre cut acrofs the fibres of vege- 
table or animal fubftances,, either in their natural or artificial 
breadths (as boards ), or by reducing natural or artificial thin 
tubes of them into helices . By threads I mean the fame kinds 
of fubftances taken lengthwife 7 either from their being natu- 
rally in thin threads, or by reducing them to that ftate, in 
3 tearing 
