128 7. C. Mendenhall—Acceleration of Gravity at Tokio, Japan. 
Deleuil, both of which ought to be correct at 0°. The result 
of these comparisons was such that a correction of —-04 mm. 
was made upon the length of the measuring rod at 0°. The 
pendulum was suspended in a small room favorably situated 
as regards all disturbances from air currents and sudden 
changes in temperature. From this room wires were carried 
to the chronograph, which was ina room near by. The time 
was taken from a break-circuit chronometer in the transit room 
of the observations recorded below. The results given are the 
periods of vibration in mean solar time, corrected for chronom- 
eter rate and also for are of vibration, the latter being observed 
by means of a scale and a telescope about fifteen feet away. 
The mean arcs varied, in the different experiments, from 40’ 
to 70 : 
After having found the total length of the pendulum, as 
well as the dimensions and masses of its various , the 
“reduced length,” or the length of the equivalent simple pen- 
dulum, is computed by means of a well-known formula. Mis 
with the time of vibration gives the value of “g” in air, and to 
this must be added the correction for “buoyancy,” In most 
of the earlier determinations by this method this correction was 
found by simply comparing the density of the pendulum with 
that of the air in which it vibrated. Although it was shown, 
before Borda made his experiments, that this correction was 
too small, he seems to have been ignorant of the fact, and not 
