C iM J 
I placed this Rod, at firft, perpendicular to the 
Horizon; betwixt two Pieces of Wood of the fame 
Thicknefs, and nailed againft the Cieling of my 
Room ; but then I had one Side only expofed to the 
Air : However it aded tolerably well, which encou-' 
raged me to try to make it more perfed; as you It 
find delineated Tab. I. Fig. 3. and Fig . 4. 
Both thefe Deal Rods were placed againft the del- 
ing of my Room with Brackets, and were buttoned 
down into fquareMortifes in each Bracket with fmall 
Pieces of Deal, that fitted their Tops exadly. Hereby 
all their four Sides became expofed to the Air ; and 
the only Difference between them is, the increafmg; 
the Effed of their Variation by two different Me- 
thods. 
To the Rod at Fig . 3. I added two Levers : The 
firft of which ABF) had its fhorter End A B but 3 
Inches in Length, and its longer BT) 125 confe- 
quently the End F> moved through 4 times the Space 
that the End A did. 
The fecond Lever EFG L fixed to ad with the 
other before-mentioned. The fhorter End EF of this 
Lever was 3 Inches, and the longer End F G, 45 
Inches; whereby the Effed of the other Lever was 
increafed 15 times, and that of the Deal Rod 60 
times. So that if the Rod lengthens but one Tenth 
of an Inch, the Point of the Lever G moves 6 Inches 5 
and if the Rod lengthens but one Inch, the Point G 
moves 60. 
The longer End of the fecond Lever in Fig. 3. 
mult be made fo much heavier, that it may move 
down freely by its own Gravity whenever the Bar 
fhortens. 
To 
