moveable roundel are the houres, this turnes with the gnomen, whose right side answereth to the middle point where there must be a nayle with a hole; through which a man may see. The use of this night diall is this: We set first the foot to the twelfth houre on the moveable roundel, and to the day of the yeere, on the undermost unmovea∣ble roundel, and set the Instruments hight, with the lowest corner of the foot A B, so that it stand water-pas, in such sort, that a man may see the North-star through the hole of the nayle, turning the diall up and downe, so long till the hinder wheeles of the great Wagon come into the diall, which being so, the gnomen shall shew the houre on the moveable roundel. And if in place of the hinder wheels of the Wagon you take the brightest of the watchtmen, it will be 4 hour. 15 minut. later, as the diall will shew, because the wheeles aforesayd of the great cart goe so much before the wayters.
Men may finde the houre by the ascension of the Sunne and the Starres in this manner; when we see any Star in the South, whose just ascension is knowne, and that we know the true ascension that day, then draw the ascension of the Sunne from the ascension of the Star, the remain∣der we devide into houres by 15, (for 15 degr. make 1 houre) and this wil be the right houre of the time, but if the ascension of the Sunne be more then the Stars, in that cause you shall add 360 degrees to the ascension of the Star, and then to as aforesayd.
I. Example.
On the 10 of April, in the evening, in the south, Ise the heart of the Lyon, whose right ascension is 147 degr. the ascension of the Sunne on that day is 19 degr. take those from the ascension of the Star, there remaines 128 degrees, and these devided by 15, I finde 8 houres, 8 de∣grees over plus, and for as much as 15 degrees make one houre, every degree will make 4 minutes, the 8 degrees over plus, make 32 minutes of an houre, it will be than at that time 8 houres, 32 minutes from the noone tyde.
II Exempel.
ON the 5 of November in the night I finde in the south the Star Aldebaran, the south eye of the Bull, whose right ascension is 64 degrees: the Sunnes right ascension on that day 220 degr. which is more then that of Aldebaran, therefore I add to the ascension of the Srar 360 degrees, it makes 424 degrees, the Sunnes right ascen∣sion being taken from this, there remains 204 degr. which is the difference betweene the ascension of the Sunne and the Star aforesaid, which being devided by 15 you shall finde 13 houres, 8 degrees, which make 36 minutes, it is then 13 houres 36 minutes from the noone tijde, that is 1 houre, 36 minut. after midnight.
How to finde the ascension on any day in the yeere of the Sunne and the Stars, we have here adjoyneth 2 tables, the one of the Sunne, showing from 5 dayes to 5 dayes, the Sunnes ascension, out of which you may easily finde the same in other dayes. The other for thirtie of the primest fixed Starres, both of them onely by degrees, that being sufficient for this businesse.