Hygromciry . 2 3 
with great irregularities. Here then we fee two oppofite e fired s 
of moifiure \ one which lengthens the fibres ; the other which, 
by / welling the twified firings, Jhortens them ; and we lee 
thofe efFeds follow different laws, from which is produced a 
retrogradation that we may change ad libitum . 
35. Now, the texture of animal and vegetable fibrous fub- 
flances mufi be a fort of reticle , which exifls in thofe which 
are naturally in thin threads , and in the mod minute fiaficicuii 
that we can feparate from a mafs ; and we fee it in the la ft cafe, 
for in fubdividing thofe fiaficicuii , there are always fibres break- 
ing in the points where they were anaflomofed with others; 
confequently, the primary fibres of thofe fubflances form be- 
tween them mejhes fimilar to thofe of a net ; and thofe mejhes , 
which are widened by the introdudion of water , muft produce 
in the threads the fame effed as the iwifi in the above firings , 
36. If then moifiure , in ading on vegetable and animal 
threads , natural and artificial, produces on their length two op- 
polite effedls ; one of which, fmall at firfl but increafing gra- 
dually, compenfiates at fome period the other which is firffc 
vifible, and furpajfies it afterwards, fooner or later, according to 
the nature of the threads ; it is evident, that they cannot be 
proper for the hygrometer •, fince, from the indication of fome 
of them it might fometimes be concluded, that moifiure 
changes in one fenfe, while it really changes in the contrary 
fenfe ; and from fome others, that moifiure is extreme , long 
before it is really fo. As for th efiips ; fince moifiure has only 
one effed on their length , that of widening more or lefs the 
mefioes of the crofis fibres, I concluded ; that all their hygro/copic 
indications, in every part of their fcale, were true in refped of 
increafie and decreafe of moifiure ; and that confequently, that 
clafs of hygrofcopes might be depended upon on that important ' 
point. 
