DIAL 
dials, is very rare; the geometrical and trigonometrical con- 
Reaction of thefe lat, therefore, as a _— intricate, 
we here choofe to omit, and refer y have a fancy 
for fuch a dial, to an univerfal roe ata iaitad of drawing 
all kinds of dials here fubjoined 
An eafy method of dcferibing a Diau on any hind of plane, by 
IAL, or circle —Suppole, e. gr.a dia 
: : the plane 
a moveable, affume ca “merci at pleafure. 
by means of the pense EKF, 
orld ‘Cabich i is had 
F be a to the hecitn of the pole), 
GI be 
ifthe angle K E 
dial hang over the me- 
the 12 o’clock line on the d 
fively applied tothe axis GI, fo as the fhado 
dex, or ftyle G I, falk upon one hour-line after another ; the 
fame fhade will mark out the feveral_ hour-lines on the plane 
Wo oting the oe therefore, on the fhadow, draw lines 
through them t an index being fixed in G, ac- 
cording to the angle IGF, its fhadow will point out the 
fevera! hours by the light of the fun 
Ifa dial were required ona ated plane, having raifed 
the equinofial circle, as above directed, ee 7 rward the 
index GI, mv the tip thereof, I, touch the. 
If the plane be inclined to the horizon, ave eee of 
the pole fhould be formed on the fame ; and the angle of the 
triangle K E F fhould be made equal thereto. 
anew method of conftruiing fun-dials, for any given 
latitude, without the affiftance of ‘dialling fcales,. or loga- 
rithmic calculations, by Mr. 
vol, lvii. for 1767, art. 36, and in his Sele& Exercifes, p. 95. 
Note. Befide the feveral {pecies of dials above-mentioned, 
with are faid to be with centres, there are others, called 
dials pai: eee See CENTER of a Dial. 
o he made for 
fies. the elevation of whofe pole is ite very {mall, or 
very grea 
Dias, Vertical, without centres, are for places, the eleva- 
tion of whofe pole is very grea 
Diaus, For the furniture of. “See Furniture. 
See Horodiical oo 
Diar, Reflecting. See REFLECTING 
Diar, Cylindric, is reprefented in Plate NE i Oe ce ey 
This dial may be delineated cn paper, and then pafte ‘d 
round a cylinder of wood, and it will thew the time of the 
day, the fun’s place in the ecliptic, and his altitude at spe 
time of obfervation. Draw the right line aA B (fg. 2 
parallel to the top of the paper, and with any opening of 
the compaffes on the centre a deferibe the quadrant A 
and graduate it. Draw the right line AC at right angles 
AB, and touching the quadrant A E at the point A. 
From the centre a draw right lines through as many de- 
grees of the quadrant as are equal to the fun’s altitude at 
noon, on the longeft day of the year, at the place for which 
3 which altitude at London is nearly 
bo 
_—— 
‘ftraight lines acrofs the paper, parailcl to the firft right line 
A B, and thefe will be the parallels of the fun’s altitude in 
‘whole degrees, from fun o fun-fet, on all the days of 
n-rife t 
the year. Thefe parallels of gue mutt be drawn out to 
Vou, XI. 
Fergufon, in the Phi]. Tranf.. 
BD, at top and 
ottom, into twelve equal parts, for the twelve figns of the 
ecliptic; and from one mark to the oppofite co draw 
right lines parallel to AC and ; and place the cha- 
of the twelve figns in the twelve fpaces at i bot- 
tom, beginning with VS Capricorn, and ending with 
Pifces. Thefe {paces fhould ieee be divided by parallel 
lines into halves and quarters. At the top of the dial make 
a fcale of the months and days of the year, fo that the days 
may ftand over the fun’s place, found in an Ephemeris, for 
each of t in the figns of the ecliptic. Compute the 
fun’s ahaa for every hour, in the latitude of your place, 
t it from a table, when h 
middle, end fizn of the ecliptic; and in 
the upright parallel ales at the beginning and middle 
of each fign, mak s for thefe altitudes among the 
Bonizental ‘parallels, reckoning ‘downward in - 1€ ores of 
may alfo be taken and laid down for the half hours and 
quarters. Then cut off the paper at the left-hand on which 
the quadrant was drawn, clofe by the right line AC, and 
all the paper at the right-hand, clofe by the right line 
B D, and cut it alfo clofe by the top and bottom horizontal 
lines, are it will be fit for patting round the cylinder, This 
cylinder, as 24.) is hollow for holding the ftyle DE, 
i t-ufed. The ftyle mutt ftand out, ea: 
cular to the “ide of the cylinder, juft over the right line 
. 28,) where the parallels of altitude begin, and its 
€ point ¢ from the cylinder, muft be 
ig. 28.) 
» (F8 
length, or diflance of the 
equal to the radius aA o 
middle of t sylinter’ and then the point, or loweft en 
f the fhadow, will fall upon ce time of the day, as it is 
before or after noon, a the curve hour-lines, and will 
what fign of the ecliptic the fun is at that 
time, and the pe ee may be nearly eftimated by the eye. 
sre 
nthe fun is in the equinoGial, and has no decli- 
nation, a altitude may be eafily found by the following 
proportion. As radius is to the cofine of the latitude, fo is 
the cofine of the hour from noon to the fine of the altitude : 
but if he has north or fouth declination, fay, as radius is to 
the fine of the declination, fo is the fine of the latitude to 
the fine of the fun’s altitude at fix o’clock. For the fun’s 
altitude at other hours the two following proportions muft 
e ufed, wiz. 1. As the cofine of the hoursffom the me- 
ridian to radtus, fo is the tangent of the latitude to the tan- 
gent of a fourth arc, from which the declination i is to be 
declination, added to the fourth arc, muft be 
os arc, when they — a quadrant, in finding the alti. 
des be Sore and after fi 
2, As 
