[ 37 ° ] 
farther diftant from the other than ten inches. If 
the distance was greater, the fire then began to di- 
verge, and lofe part of its force 5 and this force di- 
minifhed in proportion to its divergency, which was 
nearly as the diftance of the two plates. 
The difficulty however of applying the Torricel- 
lian vacuum to thefe experiments has been happily 
got over by the right honourable the Lord Charles Ca- 
vendifh, our worthy Vice-prefident. This noble lord, 
•who to a very complete knowlege of the fciences joins 
that of the arts, and whofe zeal for the promotion of 
true philofophy is exceeded by none, has applied it in 
the following manner, and his lordffiip has had the 
goodnefs to put his apparatus into my hands. This 
apparatus confifted of a cylindrical glafs tube of about 
three tenths of an inch in diameter, and of feven 
feet and half in length, bent fomewhat like a para- 
bola in fuch a manner, that thirty inches of each of 
its extremities were nearly ftraight, and parallel to 
each other, from which an a r ch fprung, which was 
likewife of thirty inches *. This tube was carefully 
fill’d with mercury : and each of its extremities being 
put into its bafon of mercury, fo much of the mer- 
cury ran out, until, as in common barometrical 
tubes, it was in equilibrio with the atmofphere. 
Each of the bafons containing the mercury was of 
wood, and was fupported by a cylindrical glafs of 
about four inches in diameter, and fix inches in 
length ; and thefe glaffes were fatten'd to the bot- 
tom of a fquare wooden frame, fo contrived, as that 
to its top was fufpcnded by filk lines the tube filled 
with 
* See the reprefentation of this apparatus, Tab. XVI, 
