310 G) OGRAP}Y AND ASTRONOMY. Problem XXVIII. " How to transfer a meridian line from one place to another." There are several ways of doing this. 1st -Way. If it be on the same plane, make a parallel line to it, and that is a true meridian. IId Way. If it be required on a different plane, set some good horizontal dial at the true hour and minute by your meri- dian line on the first plane, then remove it and set it to the same minuteon the second plane, and by the 12 o'clock line mark your new meridian. Note, If the sides or edges of your horizontal dial are cut truly-parallel to the 12 o'clock line, you may drawameridian by -them as before. IIId Waÿ. Hold up a thread and plummet in the sun, or set up a perpendicular style near your Meridian line any time of the day, and mark what angle the line of shadow makes with that meridian line on your first plane ; then at the same mo- ment, as near as possible, project a line of shadow by the thread, or another perpendicular style on the new plane, and set off the same angle from it which will be a true meridian. Note, Two persons may perform this better than one. Problem XXIX. " How to draw a line of east and west on a horizontal plane." Where a meridian line can be drawn, make a meridian line first, and then cross it at right angles, which will be a true line of east and west. But there are sonic windows in a house on which the sun cannot shine at noon ; in such a'case you may draw a line of east and west several ways. Ist Way. You may use the same practice which problem XXII. directs, with this difference, viz. instead of seeking the sun's azimuth from the south, seek its azimuth from east and west, and by a line of shadow from a thread and plummet marked at the same time, set off the angle of the sun's azi- muth from the east in the morning, or the west in the after- noon. A common observation of the course of the sun will sufficiently inform you on which side of the line of shadow to set your angle. lid Way. You may use the seoond method of transferring a meridian line by a horizontal dial with this difference, viz. in- stead of using the 12 o'clock hour line; by which a meridian was to be drawn, use the ü o'clock line, which will be east and west ; for in a horizontal dial it stands always at right angles with the meridian. IIId Way. The third method of transferring a meridian line will serve here also; hut with this difference, viz, set off the .eompletnent of the angle, which the line of shadow makes with
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