g power produces no perceptible difference in the
time. To prevent the injury of the conical pendulum and the wheel work
by any sudden check of the cylinder, a ratch-wheel connexion is placed
between the cylinder and the train of wheel work; this enables the
pendulum to run on until it gradually comes to rest. The pendulum,
which weighs about 18 lb, is compensated, and makes one revolution in
two seconds; it is suspended from a bracket by means of two flexible
steel springs placed at right angles to one another.

The observatory of Washburn, University of Wisconsin, is furnished
with a chronograph of the same type as that of Dent (_Annals Harvard
Coll. Obs._ vol. i. pt. ii. p. 34), but in this instrument the
rotation of the cylinder is controlled by a double conical pendulum
governor of peculiar construction. When the balls fly out beyond a
certain point, one of them engages with a hook attached to a brass
cylinder which embraces the vertical axle loosely. When this mass is
pulled aside the work done on it diminishes the speed of the governor.
The pendulum ball usually strikes the hook from 60 to 70 times per
minute. Governors on this principle were adopted by Alvan Clark for
driving heliostats in the United States Transit of Venus Expedition,
1874.

Grubb.

In the astronomical chronograph designed by Sir Howard Grubb (_Proc.
Inst. Mech. Eng._, July 1888), the recording cylinders--two in
number--are driven by a weight acting on a train of wheel work
controlled by an astronomical telescope governor. The peculiar feature
of this instrument is that the axle is geared to a shaft which
communicates motion to the cylinders through a mechanism whereby the
speed of rotation is constantly corrected by a standard clock. Should
the rotation fall below the correct speed it is automatically
accelerated, and if its speed of rotation rises above the correct one
it is retarded. The accelerator and retarder are thrown into action by
electromagnets, controlled by a "detector" mounted on the same shaft.
The rather complicated mechanism employed to effect the correction is
described and fully illustrated in the reference given. The cylinders
are covered with paper, but all the markings are made with a
stylographic pen. The marks indicating seconds are dots, but those
made by the observer are short lines. When an observation is about to
be made the observer fir