^•g Mr. de Luc on 
and I found a very little difference in its expanfon, comparatively 
with what had appeared from my firft experiment. Then, 
continuing the fame trial on various fubftances, I found the 
effed of different temperatures of water very fmall in general ; 
and even in fome fubftances, as deal taken length wife, and 
hemp, I could not afcertain any. 
Thefe experiments led me to think, that the fmall 
variations produced by beat in hygrofcopic fubftances dipt in 
water, were not hygrofcopic modifications, but the mere effects 
of heat, by the ceffation of all hygrofcopic modifications ; thele 
having then attained their maximum: which is a difcrimination of 
-effeds, that I had vainly attempted to produce by other means. 
When afterwards I had found the method of producing extreme 
drynefs, I made a lime apparatus, for the purpofe of repeating 
in it the fame experiments with my compound frames ; and 
1 found that theory confirmed, by the effeds of heat in 
that apparatus being nearly the fame, on the fame fubftances, 
-as when they were in water. 
26. From the whole of the foregoing experiments there 
cannot remain any doubt, that water, in its liquid ftate, is a 
fare means of fixing the point of extreme moifture on hygrometers. 
Particularly, in refped of elaftic fubftances, as ivory, quill, 
whalebone, all forts of wood, and a number of others which I 
have tried, the laft experiments in water of different tempera- 
tures, afford an immediate proof, that their faculty of fucking 
water has a fixed limit, proceeding from a final rejiftance of their 
pores, to be more dilated by the introdudion of water. Conse- 
quently, their utmojt expanfion is a true fign, that moifture is 
extreme in them ; which point cannot be exceeded. But my 
propofition extended farther : 1 had faid, that water was the 
mly certain means of obtaining immediately the point of 
^ extreme 
2 
