HOROLOGY. 
S3 2 
it is prefumed the preceding detail, clearly underllood, will 
render the reft perfectly intelligible without further expli¬ 
cation- We have here elucidated the mode of chiming the 
jooth Pfalm in preference to any other tune, becatile in 
Derham’s Artificial Clo.ckmaker, publilhed in 1714, ' the 
notes of this pfalm,which he gave as an example, were un¬ 
fortunately wrong pricked down, and the barrel was wrong 
marked all’o ; thefe miltakes were copied into Chambers’s 
Cyclopaedia ; thence, with a few additional blunders, into 
the Encyclopaedia Britannica ; and fo on into all the ab¬ 
breviations and imitations of thofe excellent works. 
When the hammers are very heavy, as in church-clocks, 
thole bells which have quavers or femi-quavers of the 
fame note, to be (truck immediately in fuccellion, require 
to have each two hammers and each a pair of parallel cir¬ 
cles pricked to perform within the limit of time; but this, 
is not required in common houle-clocks; for, where the 
mechanifm is light, the hammers may be made to aft with 
as much rapidity as the jacks of a harplichord. 
This method of pricking a chime-barrel for playing on 
bells differs from that of an organ-barrel in this refpeft; 
that in the former the length ot the note is meafured by 
the fpace between the contiguous pins, whereas in the 
latter the limit of the note is produced by crank-pieces, 
inltead of pins, which pieces keep the pipes open, and 
therefore muft cover the very lpaces which lie between 
the pins of the other, the projecting parts of one barrel 
mutually correfponding to the vacant parts of the other. 
The ingenious Dr. Franklin contrived a clock to (how 
the hours, minutes, and feconds, with only three wheels 
and two pinions in the whole movement. The dial-plate, 
fig. 67, Plate XI. has the hours engraven upon it in lpiral 
fpaces along twrn diameters of a circle containing four 
times 60 minutes. The index A goes round in four 
hours, and counts the minutes from any hour by which 
it has palled to the next following hour. The tin e, 
therefore, in the polition of the index Ihown in the figure 
is thirty minutes pall either XII. HIT. or VIII. and fo in 
every other quarter of the circle it points to the number 
of minutes after the hours which the index laff left in its 
motion. The fmall hand B, in the upper circle, goes round 
once in a minute, and (hows the feconds. A plan of the 
wheel-work of this clock may be feen in fig. 68. A is 
the firff or great wheel, containing 160 teeth, and carries 
round in four hours, the index A, in fig. 67, let down 
through a hole on its axis. This wheel turns a pinion B, 
of ten leaves, which therefore goes round in a quarter of 
an hour. On the axis of this pinion is the wheel C, of 
120 teeth; which goes round in the fame time, and turns 
a pinion D, of eight leaves, round in a minute, with the 
feconds hand B, of fig. 67, fixed on its axis, and alfo the 
wheel E of 30 teeth, for moving a pendulum (by pallets) 
that vibrates feconds, as in a common clock. This clock 
is wound up by a line going over a pulley on the axis of 
the great wheel, like a common thirty-hour clock, as 
Ihown at F, fig. 68. Many of thefe fimple machines have 
been conltrufted, which meafure time exceedingly well. 
It is fubjeft, however, to the inconvenience of requiring 
frequent winding by drawing up the weight; and likewile 
to lome uncertainty as to the particular hour Ihown by 
the index A. 
Mr. Fergufon propofed to remedy thefe inconveniences 
by the following conltruftion. In the dial-plate of this 
clock, fig. 69, there is an opening abed, below the cen¬ 
tre ; through which appears part of a fiat plate, on which 
the 12 hours, with their divillons into quarters,’are en¬ 
graved. This plate turns round in 12 hours; and the 
index A points out the true hour, &c. B is the minute- 
hand, which goes round the large circle of 60 minutes, 
whiift the plate abed lhifts its place one hour under the 
fixed index A. There is another opening efg ,; through 
which the feconds are feen on a fiat moveable ring at the 
extremity of a fleur-de-lis, engraved on the dial-plate. 
The plan of the wheel-work of this clock may alfo be 
.readily conceived from fig. 68. A Ihows the great wheel, 
containing 120 teeth, and turning round in 12 hours. 
The axis of this wheel bears the plate of hours, w'hich may 
be moved by a pin pafling through fmall holes drilled in 
the plate, without affecting the wheel-work. This great 
wheel A turns a pinion B of 10 leaves round in an hour, 
and carries the minute-hand B on its axis round the dial- 
plate in the fame time. On this axis is a wheel C, of 120 
teeth, turning round a pinion D, of fix leaves, in three 
minutes ; on the axis of which there is a wheel E, of 90 
teeth, that keeps a pendulum in motion, vibrating feconds 
by pallets, as in a common clock, when the pendulum- 
wheel has only 30 teeth, and goes round in a minute. 
In order to fliow the feconds by this clock, a thin plate 
mull be divided into three times 60, or 180, equal parts, 
and numbered 10, 20, 30, 40, 50, 60, three times luccef- 
fively ; and fixed on the fame axis with the wheel of 90 
teeth, fo as to turn round near the back of the dial-plate ; 
and thefe divifions will (how the feconds through the 
opening cf gh, fig. 69. This clock will go a week with¬ 
out winding, and always (how the precife hour; but Mr. 
Fergufon candidly acknowledges, that it ha's two difad- 
vantages, from which Dr. Franklin’s clock is free. When 
the minute-hand B, fig. 69, is adjufted, the hour-plate 
mull alfo be fet right by means of a pin; and the fmall- 
nefs of the teeth in the pendulum-wheel will caufe the 
pendulum-ball to deferibe but fmall arcs in its vibrations; 
and therefore the momentum of the ball will be lefs, and 
the times of the vibrations will be more affected by an 
unequal impulfe of the pendulum-wheel on the-pallets. 
Befides, the weight of the flat ring on which the feconds 
are engraved, will load the pivots of the axis of the pen¬ 
dulum-wheel with a great deal of friftion, which ought 
by all pollible means to be avoided. To remedy this in¬ 
convenience, the fecond plate might be omitted. A clock 
fimilar to Dr. Franklin’s was made in Lincolnlhire about 
the end of the 17th century; and is now in London in 
the poffeflion of a grandlon of the perlon who made it. 
Mudge fays, that clocks of the fame kind were uled in 
Tompion’s houfe; fo that he reckons the invention by no 
means new. 
A clock, Ihowing the apparent diurnal motions of the 
fun and moon, the age and phafes of the moon, with the 
time of her coming to the meridian, and the times of high 
and low water, by having only two wheels and a pinion 
added to the common movement, was contrived by Mr. 
Fergufon, and deferibed in his Seleft Exercifes. The 
dial-plate of this clock as Ihown in the lame plate, at 
fig. .70, contains all the twenty-four hours of the day 
and night. S reprefents the Sun, which ferves as the 
hour-index, by going round the dial-plate in twenty- 
four hours; and M the Moon, which goes round in 
twenty-four hours fifty minutes and a half, the time of 
her going round in the heavens from one meridian to the 
fame meridian again. The Sun is fixed to a circular 
plate, as Ihown at fig. 71, and is carried round by the 
motion of that plate on which the twenty-four hours are 
engraven ; and within them is a circle divided into twenty- 
nine and a half equal parts for the days of the moon’s age, 
reckoning from new moon to new moon; and each day 
Hands direfll'y under the time, in the twenty-four hour 
circle, of the moon’s coming to the meridian; the XII 
under the Sun Handing for noon, and the oppofite XII 
for midnight. The Moon M, is fixed to an inner circular 
plate, fig. 70, of the fame diameter with that which carries 
the Sun, part of which may be feen through the opening 
over which the fmall wires a and b pals in the moon-plate. 
The wire a (hows the moon’s age and time of her coming 
to the meridian, and b (hows the time of higll-water for 
that day in the lun-plate. The diltance of thefe wires 
anfwers to the difference of time between the moon’s 
coming to the meridian and high-water at the. place for 
which the clock is made. At London their difference is 
two hours and a half. Above the moon-plate there is a 
fixed plate N, fupported by a wire A, fixed to it at one 
end, and fixed at right angles into the dial-plate at the 
midnight 
