DIAL. 
I. o'clock; draw another line at 24°!, which 
will give the place of II. o’clock ; through 
38" Jj will give the place of III. o’clock; 
through 53° 1 for IIII. o’clock; through 
71°.^ for V. o’clock; and the line crossing 
your meridian, will give VI. o’clock. The 
base of your gnomon is to be equal to a 
radius of the inner liour circle, having the 
altitude of tlie place you are at for its angle : 
thus the gnomon in this figure would have 
b k, its upper line, standing at an angle of 
51° i from its base line ab; the lowest part 
being set on to the centre of the VI. o’clock 
line, even witli the meridional line, and 
the broadest (i. e. highest) part of the gno- 
mon a k, being towards the hour of XII. 
The left, or morning side of the hour table 
is made by drawing lines, at the angles 
already described, from the centre f, 
through its appropriate quadrant. The 
hours before VI. in the morning, and after 
VI. in the evening, are adjusted by con- 
tinuing through the centres 6 and d, re- 
spectively, those lines which indicate their 
ascertained numbers : thus the line of V., 
P. M., continued tlirough the centre d, w’ill 
give the place of V., A. M. 
This dial must be placed exactly hori- 
zontal, and its XII. o'clock point, i. e. the 
meridional line, must be precisely north- 
ward. The most certain mode of laying 
the meridian truly north, is by observation 
of the polar star; or by taking an obser- 
vation at XII. at noon, by means of a quad- 
rant, when the exact moment of the sun’s 
utmost altitude for the day being ascer- 
tained, the shadow thrown upon a plane, 
by means of a thin cord sustaining a heavy 
plumb, will give a correct northern line, 
either on the dial plate, already so far pre- 
pared on its base, or on any otlier level 
surface, from which a true parallel may 
be taken. With respect to adjusting by 
aid of a compass, it cannot be recom- 
mended : those instruments are often faulty, 
and when they are not so, the variation is 
not always exactly laid down. 
To construct a horizontal dial by means 
of a terrestrial globe, elevate the pole to 
the latitude of the place, and bringing the 
nearest meridional line to the brazen me- 
ridian, set the index to XII. uppermost. 
Now turn the globe until the index comes 
exactly to I., which will be effected by a 
movement of 15° measnrc<i on the equator; 
each hour making a change of 15° on the 
sun’s place thereon ; (for 24 hours multi- 
plied by 15, make a total of 360° eqtial to 
i) wiiole circle.) Tlie place where the me- 
ridional line moves to should be marked, 
for that will give the place of I. o’clock ; 
move on 15° more, to find where the me- 
ridional line cuts the equator, for the place 
of II. o’clock ; and thus in succession will 
all the hours’ places be indicated by the 
meridian at each change of 15° on the 
horizon ; always measuring close to the me- 
ridian, or following the hour hand on the 
index. If the latter be marked witli halves 
and quarters of hours, the. corresponding 
divisions may be made on the equator, as 
the meridian by which yon are governed 
passes on, taking 71" for a half hour, and 
3|° for a quarter; but such is seldom re- 
quired, except in very large dials ; the eye 
usually judging with tolerable precision, of 
the quantity covered by the shade of the 
gnomon. 
To set this off on paper, measure the 
number of degrees between the several 
parts of the meridian, noted down as sta- 
tions of the governing meridional line, 
when passed on 15° at each movement. 
This being done from XII. to VI. will 
establish a measurement that may be imi- 
tated on any scale, observing to draw ths 
VI. o’clock line correctly, and to give a 
proper length of base, as well as a due 
latitudinal angle to the gnomon. The me- 
thod suggested by Mr. Ferguson, of filling 
up the interior of the horizon after drawing 
forth the globe, is prolix, and suits but few 
persons : whereas, tlie knowledge of how 
many degrees are included in each interval, 
respectively, proves a sufficient guide. 
Those intervals will be found to correspond 
with what have been directed in describing 
the 2nd figure. 
To make an erect dial directly south. 
Fig. 3. On tliis the sun can shine only from 
VI. A. M. to VI. P. M. ; therefore, only 
the intermediate hours need be noted. 
Elevate the pole as before directed, but in 
lieu of placing XII. to the north, place it to 
the south of your dial plate, which in this 
kind is most conveniently made an oblong, 
projected vertically below the VI. o’clock 
line. Proceed to find the places of the 
hours as before shewn, trace tliem through 
their centres to the opposite parts of the 
hour circle, for on that they are to stand. 
The gnomon is to make an angle equal 
only to the co-lalitude of the place : thus, 
if you are in 51^°, the co-latitude (being 
the amount required to complete to 90°) 
wmnld be 38 1°. 
Or you may proceed as follows ; on the 
meridional line a b, as it points downwards 
