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5 
at the Island of Balta, and.at WoolwichCommon. 427 
judge what reliance may be placed upon the principal results 
already obtained. 
It will, first, be proper to present a concise description of the 
clock. itself. The ** movement,” as it is technically called, is 
such as is usually put to astronomical clocks of the best con-_ 
struction, and has “* Graham’s dead-beat escapement,”’ with the 
pallets jewelled—this being all the jewelling which the clock has. 
The pendulum is a gridiron compensation, and is suspended by 
a spring, through an orifice in which .a steel axis passes, upon 
the middle of which it is firmly clamped between two pieces of: 
brass. The ends of this axis rest in Vs upon the top of two short 
pieces of brass, which are firmly screwed to the ‘ rising-board” 
(that is, the board upon which the clock is fixed) at about five 
inches asunder, but are so much inclined as to appreach within 
an inch and a half of each other at top; where they are connected 
by a piece of brass which is screwed to the back of each, and 
made additionally steady by two other pieces of brass, of which 
one is screwed to each of them and to the back-plate of the clock. 
The suspending spring is about one inch and a half long; half 
its length playing freely below the small horizontal axis, while 
the other half is fixed by pins in a slit at the top of the thiddle 
steel-bar that projects from “ the gridiron.’ The ball or bob 
of the pendulum is seven inches across and two inches thick at 
the middle; it weighs about fourteen pounds avoirdupois, and 
rests by its ceutre upon the “ regulating nut,” which is a cylin- 
drical brass one made sufficiently long to reach the centre of the 
ball; it is united to a brass prismatic stem which issues above 
the upper part of the ball, and proceeds to the gridiron part of 
the pendulum. The “ regulating nut” changes the length of the 
pendulum in the usual manner, by being *‘tapped’’ upon a screw, 
whose threads are about forty to an inch, and upon which one 
revolution, by elevating er depressing the bob, makes a difference 
inthe “ rate” of about thirty sidereal seconds in a day. The 
curve surface of this nut is graduated into thirty equal divisions, 
and an index screwed upon the bob points downward so as to 
show the division or portion of a thread at which the nut stands. 
Another index fixed near the top of the bob points horizontally 
to equal divisions on the prismatic stem, and shows the actual 
thread of the screw upon which the nut rests when it supports 
the bob at any assumed position. 
It having been found inconvenient, in moving astronomical 
clocks from one place to another, to have the ball of the pendu- 
lum and the rod inseparably attached to each other; these have 
been so constructed as to admit of occasional separation, To 
effect this, ‘* milled heads” have been made to the two lower 
cylindric pins, which connect the outer bars of the pendulum with 
the 
