[ 68 + ] 
enough to make all the intermediate Degrees obferv- 
able upon an Inftmment. 
Suppofe in Fig. i. Tab. II. A B a Rod of Iron at its 
natural Length by the Heat of the Atmofphere, placed 
upright upon one End 5 upon the Point of that refts 
a Bar CT) moveable on an Axis at a ; and that, by 
making a Fire about the End B of the Rod, till it 
is juft ready to melt, the Rod will increafe in Length 
A b y and confequently pufh the Bar into the Situa- 
tion c d. Now it is obvious to any one who under- 
ftarids ever fo little of Mechanics, that tho' the Elon- 
gation of the Rod Ab be even Icaroe perceptible to 
the Eye, yet if upon the Bar CT) the Diftance a A 
from the Axis to the Place where the Rod BA pufhes 
againft it be very fmall, and the other Part of the 
Bar a T) very long, the Arch T)d may be incre'afed 
at Pleafure, fo as to bear to be divided into any 
Number of Divifions that fhall be found neceffary : 
For the Arch T)d will always be to the Arch Cc in 
the fame Proportion as the Diftance C D a is to aC t, 
and likewife the Chords of thefe Arches T) d and Ab 
will be in the fame Proportion; y, is the Situation 
of the Lever on the Level 5 and if it be found inconve- 
nient to make the Arm aT) fo long, as to make very 
minute Alterations in the Length of the Rod AB 
eafily obfervabie, this Inconveniency may be readily 
removed by having a fecond Bar EF, turning on the 
Axis gy whofe Arm gE bearing up againft the Ex- 
tremity ID of the ftrft Bar or Lever, will rife with 
it, or be prefs'd down by it ,• and the other Arm gF 
being lengthen'd at Pleafure, the Arch FfwiM. be 
as large as you find convenient; or even a third and 
fourth Lever may be added. 
When 
