3 6 Mr. de Luc on 
moifture is then at its maximum. But if the lengthening of 
hygrofcopic threads in general, is the compound effect of two 
oppofite caufes which follow different laws ; it may be that, 
in fome threads , thofe caufes happen to compenfate each other 
at that very period ; by which means they are ftationary, though 
moifture continues to increafe. This was my opinion, and the 
above experiments were undertaken to verify it, firft, by com- 
paring the march of th t flips with the increafe in weight of their 
own fubftance , fecondly, by comparing the marches of different 
kinds of threads with each other, and alfo with the increafe in 
weight of their fubftance : and from that now we are to exa- 
mine the above propofition. 
54. In refpect of the flips my theory is, that as moifture 
cannot adt on their length but by widening the mejhes of their 
tranfverfal fibres, they cannot go on lengthening but by im- 
bibing more and more moifture, from its increafe in the air ; 
and this we fee to be the cafe, by comparing the marches of 
the three kinds of flips with the correfpondent increafes in 
weight of the quill and deal fhavings, during the whole pro- 
grefs of the experiment. There are differences in thofe marches 
as I expedted (§ 37*) > but they are not fuch as to give the 
fmalleft reafon to fufpedt, that afterwards, during the period 
of the three laft terms of the table, in which we have no cor- 
refpondent obfervations of increafes of weight in the fhavings 
of deal and quill, the fame law does not take place as in the 
17 antecedent terms. If the experiment was only made with 
one kind of flip, it might be objedted, that though that J lip 
lengthens regularly during the whole increafe of moifture from 
its minimum to its fuppofed maximum, it is not impofftble but 
that immediately after, by fome peculiarity of its nature, it 
will lengthen, without any farther increafe of moifture in the 
medium. 
