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.

Sect. 3.

To describe an erect, direct East Dial. See Fig. 12.

Having drawn ABCD. a rectangle para∣lellogram, fix upon any point in the lines AB. and CD. for the line of six, provided the distance from that point to A. being en∣tred radius in the line of tangents, the di∣stance from thence to B. may not exceed, nor much come short of the tangent 75. This point being found, enter the distance from thence to A. (which we shall call 6. A.) ra∣dius in the line of tangents, and keeping the sector at that gage, lay down upon the lines AB. and CD. 6. 11.=tang. 75. 6. 10=tang. 60. and 6. 9=6. A.=tang. 45. and 6. 8.= 6.=4.=tang. 30. Lastly, 6. 7=6. 5=tang. 15. draw lines from these points on AB. to the respective points on CD. and you have the hours.

To place it on the plain, draw the angle DCE.=co-latitude, and laying ED. on the horizontal line of the plain, prick off the hours.

The same rules serve for delineation of a West Dial, only as this hath morning, that must be marked with afternoon hours.