The semicircle on a sector in two books. Containing the description of a general and portable instrument; whereby most problems (reducible to instrumental practice) in astronomy, trigonometry, arithmetick, geometry, geography, topography, navigation, dyalling, &c. are speedily and exactly resolved. By J. T.

PROBL. 2.

The day of the Moneth given, to find the Suns place, declination, ascensional difference, or time of rising and setting, with his right ascension.

The thread laid to the day of the Moneth gives the Suns place in the line of signs, rec∣koning according to the order of the Moneths (viz. forward from March the 10th. to June, then backward to December, and forward again to March 10.) In the limb you have the Suns declination, reckon∣ing from 60/0 on the movable piece towards the head for North, toward the end for South declination. Again, on the line of right ascensions, the thread shews the Suns right ascension, in degrees, or hours, (accor∣ding to the making of your line) counting from Aries toward the head, and so back a∣gain according to the course of the signs un∣to 24 hours, or 360 degrees. Lastly on the line of hours you have the time of Sun rising and setting, which turned into degrees (for the time from six) gives the ascensional dif∣ference. Ex. gr. in lat. 52. deg. 30 min. for which latitude I shall make all the examples.

The 22 day of March I lay the thread to the day in the Moneths, and find it cut in the Signs 12 deg. 20 min. for the Suns place, on the limb 4 deg. 43 min. for the Suns declina∣tion North. In the line of right ascensions it gives 46 min. of time, or 11 deg. 30 min. of the circle. Lastly, on the line of hours it shews 28 min. before six for the Suns rising; or which is all, 7 deg. for his ascensional dif∣ference.