28 Different “ Rates” of Pennington’s Astronomical Clock, 
the inferior cross piece of brass to which the stem, screw, and 
bob are appended. By these means the said cylindric pins are | 
easily taken out, and the bob with its adjusting screws, &c. se- 
parated from the compensating part of the pendulum, and at- 
tached to it at pleasure: proper marks upon the pins, screws, &c. 
preventing any junction except of corresponding parts, after a 
tompareny separation has taken place. 
This description will, perhaps, be rendered more perspicuous 
by a reference to Plate IV. fig. 1: op, rs and mn, are the hori- 
zontal pieces, to which the nine vertical bars of the pendulum 
are attached. The two exterior bars are attached to the cross 
piece mn, by the milled-head cylindric pins, which enter where 
two dots are marked in the figure between m and m: when those 
pins are taken out, the cross-piece mn with all that is below it 
is susceptible of complete separation from the upper part of the 
pendulum; and each part then packs in a stuffed box, of which 
the relative fitting is so nice as to allow of neither shake nor 
strain. AB is the bob or ball of the pendulum, as before re- 
marked, seven inches across. It is so perforated as to admit 
the prismatic stem x % to enter at x, while the screw passes out 
below I’. The regulating nut a@ 0 is 1-4 inch across, and carries 
on its rim thirty equal divisions. Another smaller nut cd ¢ d, 
of which cd is 1+1 inch, and ¢ d’ 0-5 inch, is placed below the 
former; and was intended to keep it steady in travelling. Its 
thickness is three-tenths of an inch, and its weight is less than 
three-quarters of an ounce. Its weight and dimensions are given 
thus particularly, for a reason which will appear in the sequel. 
The indexes [ and I’ point to divisions on the upper stem and 
lower nut respectively; and when the parts are separated at m7, 
the previous divisions at which I and I’ stood are carefully re- 
gistered, that the pendulum may be accurately restored to its 
former state with regard to length, before it is again permitted 
to vibrate permanently, with reference to an experiment. 
To the vertical back of the mahogany clock-case is screwed a 
graduated metallic arch GR, near which the pointed inferior 
extremity of the screw vw, swings during the oscillations of the 
pendulum ; the arch GR serving by this mean to measure the 
extent of those oscillations. To the bottem of the clock-case 
are screwed three strong feet of cast-iron, which project hori- 
zontally ; near their exterior extremities they are met by three 
strong brass bars, which proceed downwards in slanting directions 
from the sides and back of the clock-case: the several extre- 
mities of these bars and of the horizontal feet, being screwed 
firmly to each other, and to the clock-case, give to the whole 
such a degree of stability as.admits of no perceptible effect from 
the vibrations of the pendulum. By means of nuts and screws 
to 
