DIAL 
on the other) and fet the characters of the aa to their 
proper lines. Fergufon’s Leétures, &c. Le& 
1A ortzontal, is that defcribed on a fofeoul plane, 
ora plane para to the horizon 
n may iluminate an leg plane at all 
times of the year, while heisa orizon ; an horizor- 
tal dial may fhew all the ee of ren ardbcial day throughout 
the year: fo that a more perfe& dial than this kind cannot 
be required. 
To deferibe an horizontal Dia. Sodas cally. —Dra 
meridian Jine AB . 8.) on the given immoveable ean: 
or affume it at pleafure, ona moveable one. 
ine. 
From a point taken at pleafure, as C, erect a perpendicular 
CD, and make the angle CA D equal to the elevation of 
the pole. ln Dm ake another angle C D E, equal likewife 
to the elevation of the pole, and draw the right line D E, 
meeting in hen make EB equal to ED, and 
trom the centre B, with the an EB, deferibe a quadrant, 
E ‘ which se _ fix equal dale 
the right line G H, cutting AB at 
See Meripian 
8 e 
e G H, in a Lipa 1,6, c,d,H. From E, ie the 
ff the intervals Ea, Eb, &c. 
from E to e, from Eto f£, Ec from Etog, ke. ion 
the centre A deferibe a little circle, and applying a little 
ruler to A, and the little points of divifion a,b, c,d, H d 
e, f. g, &, G, draw the lines A XI, A X, A IX, A VIII, 
AVII, and AT, AI, ATM, ALIV, AV. Through A 
draw a right line VI, VI, perpendicular to A B. Continue 
the right line A VII, beyond the a: ae to VII, AVIII 
to ; to Vy, and ound the whole 
x an index, making an angle 
equal to ne elevation of ~ ag : oF + Cer 
cular ftyle equal to CD; ka Pps plate 
ADE toe aeicalgs to the Dane of the oa In this cafe, the 
lines, A XI, AX, AIX, &c. are the hour-lines of the fore- 
noon; and AI, ATI, A ne &c. thafe of the sega ; 
and the fhadows of any o nomons, or ityles above- 
mentioned, at the feveral ene will fall on the ai 
hour-lines. 
To defcribe an horizontal D1au trigonometrically.—In lar 
Sciences, anno 1707, has done the world good fervice in this 
refpect ; having rendered the calculation of the hour-lines, 
which before had been operofe enough, exceedingly eafy ard 
: his canons, or analogies, we ‘hail lay down 
And, firit, for an hori- 
pole of the place being 
given to find the angles via the hou liies make with the 
meridian in sis centre aah e 
The analogy, or sas the whole fine 
radius is - aie fine ofthe sleration of cr pole of the lies, 
s diftance from the meridian, for 
C (jig. 9.) ist o DC, fo is the tangent 
the a FC, of te angle FAC. See 
feale. , 
the ‘horizontal cine and. crofs it at right anglea.b by the fix 
o’clock. 
until any one of thefe meridians cuts the horizon in the 
orth point, where the hour of XII is fuppofed to be 
aa) the reft of the meridians will cut the horizon at the 
refpective diftances of all the other hours from XII. L 
thefe points of diftance be marked on the horizon, the globe 
be removed, and a fiat board or plate,-even with the furface of 
the horizon, put into its place, then ftraight lines drawn 
from the centre of the board to thefe points will be the hour- 
lines of an horizontal dial for that latitude ; andthe gnomon 
will be i in the fituation of the axis of the globe, or make an 
e plane of the dial equal to the latitude of the 
ie ace. : 
Lona on ae Englith globe, to ime ads fet the hour 
index to the uppermoft Xlio n the horary circle ; then turn 
the Jee welivard, till the aes points asc ae! to I, ll, 
III, IV, [I in the after 
rnoon 3 or until 1§, 30, 45, 
+75,a a A ieee of the equator pal cae the brazen 
meridian; and the firft meridia: will wark the following 
degrees on the horiz: om from the north es ma the eaft, viz, 
13, 2445 38 vx» 5399 717s, and go; which are the re{peétive 
dittances of the above ee from Xil cn the plane of the 
horizon. 
In order to transfer thefe and the reft of the hours to an 
horizontal plane, draw the paraliet right lines ac and dd 
ig 10.) upon that aes at a diftance equal to the thicknefs 
e gnomon; an pace between them will be the 
meridian or r twelve fe) relock line oe At right angles 
as centres, with the 
om 
"S 
from each other, in order to enlarge the hour diftances about 
noon. ay aruler on the centre 4, and on the feveral dif. 
tances already found, wiz. 114, 244, &c. in the quadrant 
4, and draw the re {peétive afternoon hour-lines to J, IT, &c. 
As the fun rifes about four in t 
daysin London, continue the hour-lines of and V in the 
afternoon aioe the centre 4 to the oppofite fide of the 
dial. n lay the ruler on the centre a, alae the fame 
diftances, me ae a in the quadrant e ¢ 
the forenoon. 
hour-lines of XI, X, &c. and ag the 
fia ee not fet before 
ot et 
+o ot 
enufe ag parallel to the axis of the worid, when the 
dial is ane ge and will caft 
ay. of cords will fuperfede the neccflity of gradu. 
ating the quadrants. An ereé fouth dial (Plate LI. & 15.} 
is conftruéted in the fame manner, obferving . rule yi ael 
given with refpe& to the elevation of the pole, and of the 
ae and the pofition of the hours. Pergufon s Le&. 
le&t. 
- a Leribe an eens Diau mechanically, Ci the dialling 
—Draw a double meridian line 2 6, cd, 
mr 
Ole 
