The mariners magazine, or, Sturmy's mathematical and practical arts containing the description and use of the scale of scales, it being a mathematical ruler, that resolves most mathematical conclusions, and likewise the making and use of the crostaff, quadrant, and the quadrat, nocturnals, and other most useful instruments for all artists and navigators : the art of navigation, resolved geometrically, instrumentally, and by calculation, and by that late excellent invention of logarithms, in the three principal kinds of sailing : with new tables of the longitude and latitude of the most eminent places ... : together with a discourse of the practick part of navigation ..., a new way of surveying land ..., the art of gauging all sorts of vessels ..., the art of dialling by a gnomical scale ... : whereunto is annexed, an abridgment of the penalties and forfeitures, by acts of parliaments appointed, relating to the customs and navigation : also a compendium of fortification, both geometrically and instrumentally / by Capt. Samuel Sturmy.

CHAP. VIII. A South and North Erect Direct or Horizontal Dial, and how to make it.

THis belongs to an upright Wall looking full North or South, and the Plane of it lies in the East Azimuth.

First draw the Horizontal-line AB, which serveth for 6 in the morning at A, and 6 in the afternoon at B; then from the Center lay down from C the Gno∣mon of the Latitudes Complement 33. 30 both ways, as to A and B: Now with the whole Line of 6 hours from A describe an Arch towards D, and with the same di∣stance from B cross the same Arch, and draw the two Lines AD and BD, whereon from D you must transport the hours, as you see by the Figures 1, 2, 3, 4, 5. So drawing Lines through those parts from the Center C, you shall have the hours from 6 a clock in the morning to six a clock in the afternoon.

* 1.1With the Chord of 60 on the Center C describe the Semicircle ADB from which Line of Chords take the Complement of the Latitude 38, 30, and lay down from the Meridian at E unto F; so drawing CF, you shall have the height of the Stile

above the Plane. This, if it be for a large Dial, as against a Wall, is best to be made of a Rod of Iron; for small Dials a Brass Plate is best, and your Dial is done.

[illustration] geometrical diagram

This Dial shews the Hours from 6 in the morning to 6 at night: The other hours before and after 6, as far as four and eight, belong to the North face of this Dial. Because the Almicantars may oft obscure the Intersections of the Hour-circles, you may avoid that if you reduce this Dial to a Vertical Dial, for the South Horizontal Dial, being the Vertical Dial of those People who live 90 degrees Southward from us, that is, in 38 d. 30 m. of South Latitude.

Secondly, For the North face, imagine you had for the Gnomon a Wire thrust aslope through the center of the Plane from the Southside Northward, and you will presently conceive, that in the North Dial the Horizontal or 6 a clock Line will be lowest, and that the Stile or Gnomon will turn upwards towards the North Pole, as much as it turned downwards on the other side; and that all the Hours save 6 in the morning, and 6, 7, 8 at night, may be left out in our Latitude, because the Sun shi∣neth no longer upon it; and those Hour-distances you may find and set off from 6 a clock Line, as you did the Hours of like distance in the South face. Note in a South erect direct, or a South erect declining Dial, the Stile always points downwards; but if it be a North erect declining Dial, the Stile points upwards.

Notes

• * 1.1

  	90
  Lat.	51	30
  Compl.	38	30