DIAL 
or onthe other fide of aN ee sa lower emacs dial 
will only fhew the hour in autumn an 
have an aed dial, therefore dat fhall ferve all 
the year round, the upper and lowe be joined toge- 
ther ; that is, it muft be drawn on aac! fide of the plane. 
And, fince the fun fhines on one fide or on the other of an 
equinoCtial plane the nate day, fuch a dial will thew all the 
hours of an artificial day 
To deferibe an aca Diat geometrically. —The equi- 
noGtial is the firft, eafielt, and moit natural, of all dials; 
but the te of drawing it double, prevents its being 
much in uv However, as its ftru€iure 7 ake the reafon 
of the see kinds, and as it even furnifhes a mechanical 
method of drawing all the other kinds of BO. it fhall be 
here laid down. 
Firft, then, to defcribe an upper equinoiial dial: from a 
ah Cc ial ~ Dialling fg. 4. ) defcribe a ee ABDE, 
rane ters , and B E, interfe&ing each 
“ 
yt 
ilies at ite 
ngles, pare it in ies quadrants AB 
DE, and EA. Sa 
; bdivide cach quadrant into fix equal 
by the right-lines CI, CII, C III, &c. which 
lines will be hour lines. Through the centre C drive a 
ftyle, or pin, perpendicular to the plane A BD E. 
The dial thus defcribed being raifed fo as to be in the 
plane of the equator, the line C XII, in the plane of the 
meridian, and the point A lo nee te eewianda the fouth, the 
fhadow es ftyle will thew the hours both of the forenoon 
and efter 
For toe cae ‘circles include arcs of the equator of fifteen 
degrees each; confe es hed plane ABD E being 
fuppofed in the ire on he ator, the horary circles will 
likewife include arcs of 15 ee of the circle ABDE 
Wherefore, fince the angles XII C XI, XI C X, XC IX, 
&c. are ag here fuppofed 15 degrees, the lines C XII, 
XI, &e, are ooo of morary circles 
X, when in the. circle of to o’clock, &c 
Secondly, to defcribe a lower equinoGial dial: the me- 
thod is the fame as that for the upper dial, already de- 
{cribed ; except that no hour-lines are to be drawn beyond 
that of fix o’clock. 
Thirdly, to defcribe an univerfal equinoQial dial: join 
two metal, or ivory planes, ABCD, and CDEF, 
( fiz. 5.) fo as to be pee at the joint. On the upper 
furface of the plane A BC D, defcribe an upper equinoétial 
dial, and upon the lower a lovee, as ree direéied ; and 
throughs ceutre I pies a flyle. the plane DEF 
cut a an magnetic ne cedle G therein; fit on 
the fae plane a pale quadrant mea | graduated, = paff- 
ing throvugha hole cut in the pla Cc » fince 
this may be fo placed a the needle, as at the 
of the quadrant, m 
fhall be equal to the elevation of the equator ; it 
as a dial in any part of the world. When th 
the oe thefe dials can be of no ufe, 
he beft univerfal dial is that of Mr, Pardie, of which 
the sleea defcription is given by Mr, Fergufon. This 
dial confifts of three principal parts; the firft is called the 
horizontal plane A (jg. 6.) becaufe in praCtice it muft be 
un is in 
parallel to the horizon; in this plane is fixed’ an way 
pin, which enters into the edge cf the fecond a 
called the meridional plane, which is 
3 
aS) 
contains a ella - a circle a into egrees 3 in 
which part, the pin enters. The ot iv piece is a 
femicircle D, ere to the aucun, and turning in : 
by a groove, for raifing or depreffing the diameter EFo 
the femicircle, which diameter is called the axis of the in- 
ftrument. The third piece is a re G, divided on both 
fides into 24 equal parts, which are the hours. This 
circle is put on the meridional pie: 1 that ra axis 
may be perpendicular to the circle; and t 
be the common eentre of the circle, femis circle, and 
and on the other fide the laft fix months. 
figs on which the fun enters the figns, there are ftraight 
lines drawn upon the femicircle, with the charafters of the 
oe marked upon them. ‘There is a black line drawn 
uadrant, over 
o find the time of the day by this dial, it mult be 
low Pot the Gale 
a uinoctial. e upper furface of the circle will ferve 
from the 20th of March to the 23d of September; and the 
lower for the reft of the ear. 
eF of the femi- 
ircle pon I, as a centre, defcribe the circle FCG, 
n which fet off the arcs n zy qual to 234 
of each month, as found in tables of declination, mark the 
meter A B of the femicircle from a to g, 
t by the ruler; and here place the days of the 
months, anfwering to the fun’s declination. Set one foot 
of the compafles in C, and extending the other toa or g 
defcribe the femicircle a bc de fg; divide this isto fix equal 
parts, and through the points of divifion draw right lines 
parallel to CD, for the beginning of the fines (of which 
one-half are on one fide of - emi and the other haif 
3 on 
