Posthuma Fosteri the description of a ruler, upon which is inscribed divers scales: and the uses thereof: invented and written by Mr. Samuel Foster, late professor of astronomie in Gresham-Colledg. By which the most usual propositions in astronomy, navigation, and dialling, are facily performed. Also, a further use of the said scales in deliniating of far declining dials; and of those that decline and recline, three severall wayes. With the deliniating of all horizontall dials, between 30 and 60 gr. of latitude, without drawing any lines but the houres themselves.

SECT. 3.

To finde the houre of the Day.

MAke AB equall to the whole Scale, as before: and count from the beginning of the Scale to the Suns place what number of degrees there are; the same number shews the graduall distance of the Sun from the North Pole. Of this distance and the complement of your Latitude, finde the sum and

difference, and count them both upon the Scale, as was done before. Then again, count thereon also the complement of the Suns altitude: Upon which point, setting one foot of your Compasses, extend the other to the forenamed summe; and with that

[illustration]

extent upon the center B describe the arke CD. Again, setting one foot of your Compasses upon the complement of the Suns altitude, extend the o∣ther to the forenamed difference, and with that ex∣tent upon the center A, describe the ark EF. Lastly, draw the streight line DE, which only touching the two former arks, may cut the line AB in G: so shall AG (measured on the Scale, from the beginning of it) give the degrees of the Suns distance from the South. These may be turned into houres, counting 15 gr. for one houre, and 1 gr. for 4 minutes of an houre.