DOI Page / Citation link:
https://doi.org/10.11588/diglit.19574#0219
.202 D I A
Having thus found out the points in the equator, througk
which the afternoon hour lines are to be drawn, you may find
the forenocn hour diftances alfo, the fame way, viz. by remov-
ing the arch of the quadrant to the weft fide the meridian, as
before it way placed on the eaft, and bringing the firing to the
feveral 15 degrees on the weft fide the quadrant; or, otherwife,
you need only to meafure the diftances of each hour's diftance,
found in the equator from the meridian line on the cieling ; for
the fame number of hours from XII have the fame diftance in
the equinoctial line on the other fide the meridian, both before
and after noon.
The XI o'clock hour diftance is the fame from the meridian
line, with the I o'clock diilance on the other fide the meridian;
the X o'clock diftance the fame with the II o'clock diftance ; the
IX with the III, &c. and thus the diftances of all the hour lines
are found out on the eq-uator. See plate V. fig. 3.
Now, if the center of this Dial lay within doors, you might
<]raw lines from the center through thefe pricks in the equator,
and thofe lines fhould be the hour lines, as in other Dials ; but
the center of this Dial lies without doors in the air, and there-
fore not convenient for this purpofe; fo that, for drawing the
hour lines, you muft confider what angle every hour line in an
horizontal Dial makes with the meridian; that is, at what dif-
tance, in degrees and minutes, the hour lines of an horizontal
Dial cut the meridian; which you may examine as by operation
2 ; for an angle, equal to the complement of the fame angle, muft
each refpedtive hour line with the equator on the cieling have.
Thus, upon the point marked for each hour diftance in the
Cquinodtial line on the cieling, defcribe the arches I, II, III, IV,
as in the figure ; and, finding the diftance from the meridian of
the hour lines of an horizontal Dial to be according to operat. 2.
thus,
11,4c
The i 2 I hour line I 2^5 iwhofe C°mpIe".
38,14 { ment to 90 is
53>36
I meafure in a quadrant the fame radius with thofe arches al-
ready drawn from the equinodiial line.
j For the j 2 I o'clock hour I ^>4J K
I4J 136,243
And transfer thefe diftances to the arches drawn 01 the cieling;
for then ftraight line?, drawn through the mark in the arch, and
through the mark in the equator, and prolonged both ways to
a convenient length, fhall be the feveral hour lin:s, aforefaid,
and,
Having thus found out the points in the equator, througk
which the afternoon hour lines are to be drawn, you may find
the forenocn hour diftances alfo, the fame way, viz. by remov-
ing the arch of the quadrant to the weft fide the meridian, as
before it way placed on the eaft, and bringing the firing to the
feveral 15 degrees on the weft fide the quadrant; or, otherwife,
you need only to meafure the diftances of each hour's diftance,
found in the equator from the meridian line on the cieling ; for
the fame number of hours from XII have the fame diftance in
the equinoctial line on the other fide the meridian, both before
and after noon.
The XI o'clock hour diftance is the fame from the meridian
line, with the I o'clock diilance on the other fide the meridian;
the X o'clock diftance the fame with the II o'clock diftance ; the
IX with the III, &c. and thus the diftances of all the hour lines
are found out on the eq-uator. See plate V. fig. 3.
Now, if the center of this Dial lay within doors, you might
<]raw lines from the center through thefe pricks in the equator,
and thofe lines fhould be the hour lines, as in other Dials ; but
the center of this Dial lies without doors in the air, and there-
fore not convenient for this purpofe; fo that, for drawing the
hour lines, you muft confider what angle every hour line in an
horizontal Dial makes with the meridian; that is, at what dif-
tance, in degrees and minutes, the hour lines of an horizontal
Dial cut the meridian; which you may examine as by operation
2 ; for an angle, equal to the complement of the fame angle, muft
each refpedtive hour line with the equator on the cieling have.
Thus, upon the point marked for each hour diftance in the
Cquinodtial line on the cieling, defcribe the arches I, II, III, IV,
as in the figure ; and, finding the diftance from the meridian of
the hour lines of an horizontal Dial to be according to operat. 2.
thus,
11,4c
The i 2 I hour line I 2^5 iwhofe C°mpIe".
38,14 { ment to 90 is
53>36
I meafure in a quadrant the fame radius with thofe arches al-
ready drawn from the equinodiial line.
j For the j 2 I o'clock hour I ^>4J K
I4J 136,243
And transfer thefe diftances to the arches drawn 01 the cieling;
for then ftraight line?, drawn through the mark in the arch, and
through the mark in the equator, and prolonged both ways to
a convenient length, fhall be the feveral hour lin:s, aforefaid,
and,