404 Mr. de Luc on 
ftantly, if no other caufe interfered ; but it is fubjed to dif- 
turbing anomalies , which become worthy of attention within 
that fmall critical fpace which I have defcribed. The texture 
of organized hygrofcopic fubftances occafions a friction between 
their parts, when, by the changes of motflure and heat com- 
bined with their elajlicity , they undergo changes in their refpec- 
tive pofitions ; whereby they hardly can completely return to 
the very fame arrangement, though with the fame external 
circumftances ; even at extreme moijture , when, there being 
lefs friction between their particles, the greateft part of the 
difturbances produced in their former motions are reftored. To 
that general caufe of irregularity is added a particular caufe, 
when thofe fubftances are in the ftate of hygrometers ; this is 
the influence of two oppofite forces ading conftantly on them ; 
one, the tendency of their component parts to remain united ; 
the other, a weight or fpring which tends to feparate them. 
Certain accidental arrangements of their component parts give 
them more power to refift the adion which tends to feparate 
them ; and thofe arrangements are very changeable, by the 
alternate introduction and expulfion of moifure , by a long ftay 
within a fmall compafs of variations, and by more or lefs 
heat. This is a large field of fads and fpeculations, not un- 
interefting in itfelf, but on which I mu ft not dwell : what I 
have faid of thofe caufes is fufficient to account for the anoma- 
lies to which, more or lefs, every hygrometer is fubjed. But 
whereas in the flips , thofe anomalies create only fome irregulari- 
ties in the obfervations, without any deceiving confequence in 
refped of the laws of moijture, they may deceive when they hap- 
pen to interfere in the critical part of the march of fome threads ; 
forinftance, if, by a certain accidental arrangement of the con- 
ftituent parts in a flip of whalebone , there happens to be fome 
tenths 
2 
