C : 39&) 
gj 4 ooo. parts (for fo many S*** there are in 90 Bernes \ 
either in placing it , or in obferving , he (hall not miftake the 
thicknefs of a fing e thred of Silk f Headds , that Great Mru- 
ments have their defects, as the (mail ones ; ' For in thofe cbr 
sue Movable , if the thred, on which the Lead hangs, is anythin** 
big, it cannot exactly imrk Seconds 5 if it be very fine 'it breaks’ 
becaufeof us great length, and the weight of the Lead: And in 
the Fixed the greater the is, the left the Shadow 
or the Light is terminated 5 fo that it is painful enough , exactly to 
difcern the extremities thereof. Yet ’tis certain , that the create* 
the Inftruments are , .the furer AJlronomers may be : Whence it is* 
that fome Aft ohomers have made ufe of obelisks of a vaft bi°nefs 
to take the Altitudes ; 2nd Signior Cafsini^ after the example of 
Egnatio Dante , caufed a hole to be made on the higheft part of 
a Wall of 95. feet in a Church at Bononia , through which the 
beams of the Sun falling on the Floor, mark as exadlly asispof- 
fible, the height of that Luminary. 
Fifthly , Thatuhe Author reafons for the Immobility of the 
Earth after this manlier. He fuppofes for certain , that the fwift- 
nefs of the Motion of heavy bodies doth {fill increafe in their de- 
icentj to confirm which principle , he affirms to have experi- 
mented) That, if you let fall a Ball into one of the Scales of a 
Ballance , according .to the proportion of the height , it falls from 
it raifeth different weights in the other Scale. For example, A 
Wooden Ball , of i~ ounce , falling from a height of 35 inches 
raifeth a weight of 5. ounces; from the height of 140 inches a 
weight of 20 ounces ; from that of 3 1 y inches , one of 45 ounces- 
and from another of 560 inches, one of 80 ounces, &c t From this 
principle he concludes the Earth to be at Reft ; for , faith hey if it 
Ihould have a Diurnal Motion upon its Center,Heavy Bodies bein°- 
carried along with it by its motion , would in defcending defcribe a 
Curve Line , and , as he fhews by a Calculus , made by him, run 
equal (paces in equal times; whence it follows, that the Celeri- 
ty or tneir Motion would not increafe in defcending , and that 
confe-quently t ^ r ^roke would not be (Longer , after they had 
fallen thorow a longer fpace. 
ill. ANA- 
