T. C. Mendenhall— Force of Gravity, etc. 99 
Art. IX.—On a Determination of the Force of Gravity at the 
Summit of Fujiyama, Japan; by T. C. MENDENHALL. 
AN excursion to the summit of Fujiyama was made during 
the first ten days in August of the present year (1880), for the 
purpose of making a determination of the force of gravity at 
that point. In addition to four special students in physics 
from the Imperial University, the writer was accompanied by 
W. S. Chaplin, Esq., Professor of Civil Engineering, who de- 
termined the rate of the chronometer, and rendered much other 
valuable assistance. The preliminary experiments at the Uni- 
versity in Tokio, as well as those upon the mountain, were 
mainly carried out, under the direction of the writer, by Messrs. 
Tanakadate and Tanaka, who had already gained much val- 
uable experience in the determination of the force of gravity 
at Tokio. 
As stated in the previous paper, it was decided to make use 
of some form of the so-called “invariable” pendulum, and to 
compare a series of vibrations made at Tokio and at the top of 
the mountain. Owing to the difficulty of getting anything in 
the way of knife-edges made with sufficient accuracy in this 
country, nothing better could be done than to make use of a 
Kater’s pendulum by Negretti and Zambra, after removing one 
of the knife-edges, the “ tail-pieces” and all of the unnecessary 
parts. In the condition in which it was used, it consisted of a 
flat bar of brass 184 cm. long, 88 mm. wide and 4 mm. thick, 
with a knife-edge at a distance of about 15 em. from one ex- 
tremity, At nearly the lowest point was fixed the flat cylin- 
drical "weight, 10 cm. in diameter and 19 mm. thick, which was 
so of brass. On the short piece projecting above the knife- 
edge was an adjusting slide-piece which, as well as the cylin- 
drical weight, was fixed in such a way that accidental move- 
ment was rendered impossible. In order to prevent an 
possibility of entire loss of results by means of the accidental 
injury of this pendulum, while being carried to and from the 
mountain, another of nearly the same vibrating period was 
prepared, the flat bar in this case being of well-seasoned wood, 
and the cylindrical weight being of somewhat different form. 
The knife-edge used was that which had been removed from 
the Kater’s pendulum. During the month of July, both pen- 
dulums were vibrated in the Physical Laboratory of the Univer- 
sity at Tokio in the same room and from the same pier re- 
ferred to in the previous paper. Besides these two pen ulums, 
the appliances consisted, in the main, of a Negus break-circuit 
chronometer, a chronograph and a portable transit instrument 
*This Journal for August, 1880. 
