[ 293 ] 
to be the weight raifed between the fcrews and 
mawls. 
The diftance between two contiguous threads of 
each lerew was 1 j inches ; the length of the two 
oppofite levers was 12 feet 8 inches, or 152 inches, 
and defcribed a circumference of 477 ~ inches : each 
fcrew was worked by 8 men : their force, reckoned 
at 30 lb. each, makes the power working on each 
fcrew equal to 240 lb. 
Hence, from the known property, each fcrew could 
raife 65485 lb. 
And the 18 fcrews raifed 1178730 ib. 
Then there remained 570802 lb. to be raifed 
among about 126 mawls : 
Which gives 45301b, or a little more than two 
tons, to be raifed by each man with his mawl and 
wedges ; which is confiderably lefs than what I have 
feen raifed by way of experiment. 
XXXV. Obfervations on an Evenings or ra- 
ther NoEiurnal , Solar Iris. By Mr. George 
Edwards, Librarian of the College of 
Phyfcians, 
To the Reverend Dr. Birch. 
S I R, 
Read Jane Sunday evening the 5th of June 
V_^/ J 757> being walking in the fields 
near Iflington, about half a mile north of the upper 
refervoir or bafon of the New River, I obferved the 
fun 
