Burton — On the Agosta Expedition, 
113 
XVII. — An Account op Experiments upon the Motion op Yoetex 
Rings in Am. By Professor E. S. Eall. [Abstract.] 
[Read 23 January, 1871.] 
The problem discussed was the following: — A vortex ring pro- 
jected with a certain initial velocity is gradually retarded by the air ; 
according to what law does the resisting force act ? The rings were 
formed by the falling of a pendulum from a given height upon a 
2 ''cube box of the usual construction. The ring was made to impinge 
upon a target placed at different distances. The time intervening 
between the release of the pendulum and the blow of the ring on the 
target was measured by Wheatstone's chronoscope. Making proper 
allowance for the time of descent of the pendulum, the time occupied 
by the ring in travelling a certain distance was measured to the hun- 
dredth part of a second. The range of the ring, to which the experi- 
ments refer, was from a distance of four feet from the front of the box 
when the ring was moving with a velocity of 10*2 feet per second to 
a distance of 20 feet, when the velocity was reduced to 4*3 feet per 
second. 
Erom a discussion of the results it appears that the observations 
can be accounted for on the supposition that the retarding force varies 
directly as the velocity of the ring, the space {s), the time (t), and the 
velocity {v), being connected by the following equations : 
5 = 27-7 (1 -(0-69^ 0 
. «;=.^=10-2 (0-69)' 
Tables embodying the methods of reduction employed accompanied 
the paper. 
XVIII. — On Eesults obtained by the Agosta Expedition to observe 
the Eecent Solae Eclipse. By Charles E. Burton, Esq. 
[Eead February 13, 1871.] 
Agosta is a small town twenty miles north of Syracuse, on the east 
coast of Sicily. The station occupied by our party, and which formed 
the most western observatory, was immediately to the south of that of 
the Italian astronomers, and overhanging the sea, below the fortress. 
The instruments used were as follows, taking them in order from west 
to east : by Professor JF. G. Adams, of King's College, a biquartz on 
R. I. A. PROC VOL. I., SEE. II., SCIENCE. Q 
