The Third Book of the Cross-Staff

CHAP. XVII.
To Draw the Hours from the Sun-rising and Sun-setting in the former Planes.

To know how many Hours are past since the Sun-rising, or how many remain to the Sun-setting, first draw the common Hour-lines, the Equator, and the Tropicks, as before; then describe two occult Parallels of the length of the day, one for 8 Hours, and the other for 16 Hours: For so you may draw the first Hour from the Sun-rising through the common Hours of 5 in the Parallel of 16, of 7 in the Equator, and of 9 in the Parallel of 8. In like manner, the second Hour from Sun-rising, through the common Hour of 6 in the Parallel of 16, of 8 in the Equator, and of 10 in the parallel of 8. And so the rest in their order.

The first Hour before Sun-setting, or the 23 Hour from the last Sun-setting, may be drawn in like sort, through the common Hour of 3 after-noon in the Parallel of 8, of 5 in the Equator, and of 7 in the Parallel of 16. The second Hour before Sun-setting, or the 22 Hour after the last Sun-setting, through the common Hour of 2 in the Parallel of 8, of 4 in the Equator, and of 6 in the parallel of 6: And so the rest in the like order, whereof you haven another Example in the Diagram belonging to the Declining Vertical.