SECTION XX. 299 Its amplitude (or distance from east or west at its rising or setting) in summer is a c ; in winter It is t c. Here you must suppose that the sun goes down again from the meridian in theafternoon on the other side of the scheme or globe in the same manner in which its ascent toward the meri- dian is represented on this side ; so that the line M a represents the sun's semi-diurnal arch at midsummer, E,C at the equinoxes, and w s at midwinter. The semi - diurnal arch is half thearch it makes above the horizon. Note, That as we have described the various places of the sun's appearances above the horizon u- o at the several seasons of the year, so the various places of its depression be- low the horizon n o may be easily found out and described by any learner. Problem XVI. "How to represent any parallel of declina- tion on the analemma, or to describe the path of the sun any day in the year." Find out what is the sun's declination that day by some scale or table : Observe whether it be the winter or the summer half-year ; and consequently whether the declination be north or south : then for the north side of the equator, if it be summer, set the degrees of north declination upward from E toward z if it be winter set the south declination downward from E toward H and from the point of declination (suppose it be M or w) draw a line parallel to E a the equator, as M 2 -or w Vs, and it re- presents the parallel of declination, or the path of the sun for that day. ProblemXVII. " How to represent any parallel ofaltitude, either of the sun or star on the analemma. As the lines of declination are parallel tothe equator ; so the lines of altitude are parallel to the horizon suppose therefore the altitude of the sun be about 42 degrees ; set up 42 degrees on the meridian from H to A, draw the line A L parallel to no, and it describes the sun's parallel of altitude that moment. Here Note, That where the sun's parallel of declination for any day and his parallel of altitude for any moment cross each other, that is an exact representation of the sun's place in the heavens at that time : thus the point sol O is the precise place where the sun is when he is 42 degrees high on the longest day of the year : for M 0 represents his path or parallel of declina- tion that day, and A L represents his parallel of altitude that moment. I might add here also, that the prick'd archN Q s represents the hour circle in which the sun is at that moment ; and z Q D represents its azimuth or vertical circle at that time: Note, these arches are troublesome to draw aright, and are not at all neces- sary to solve common problems by the scale and compasses on the analemma.
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