Hygromctry . 419 
much increafed, it will acquire fome abfolute length ; but it 
will be fteaay again for a new point taken then in water . 
98. Another property of the flip of whalebone , which at fir ft 
(hould feem contradiftory to the former, is its great expanfli - 
bility, in which alio it furpaffes all the fubftances which I have 
tried. Such a Jhp lengthens above one-eighth of itfelf from 
extreme drynefs to extreme moijlure , which produces many ad- 
vantages in the conftru&ion and obfervation of that inftru- 
ment. In refpedt to obfervation, when it is expofed to the 
wind, the difference between the chords of the arches of its 
bends and its real length is fo fmalh comparatively with its 
hygrofcopic variations, that the indetermination of its index 
will remain confined in a Ipace of one or two degrees , when it 
becomes impoffible to obferve hygrometers whofe fubftance has 
but little expansion . Laftly, of all the fubftances which 1 have 
reduced to flips, none is fo eafily made thin and narrow as 
whalebone . I have found means for producing eafily fuch flips 
of it as, with a length of eight inches, weigh only about T ^th 
of a grain, and are thereby as quick as is convenient in other 
refpe&s. All thofe diftinftive properties of the flip of whale- 
bone feem to point out an hygrofcopic fubftance fit for our com- 
mon hygrometer . 
Deflcription of the whalebone hygrometer , 
99. I have now only to defcribe the conftru&ion of that inftru- 
meat as I have fixed it after a long experience. Thej%. 1. (Tab. 
IX/) (hews its form for common ufe, Some of thofe inftruments 
y 
are of the fame fize as the figure, and they may eafily be made 
fmailer, but commonly they are half as large again in every di- 
mention. Their frame will fufficiently be known from th t figure, 
I i i 2 therefore 
