The English globe being a stabil and immobil one, performing what the ordinary globes do, and much more / invented and described by the Right Honorable, the Earl of Castlemaine ; and now publish't by Joseph Moxon ...

OPERATION. VIII. How to make a Vertical or Erect Direct North Dial for the Elevation of London.

THERE is no difference between the Fabrick of this Dial and the former, unless it be in figuring it; for a South Di∣al reverst is a North Dial, the After-noon Hour Lines being mark't with the Morning Figures, and the Morning ones with those of the Afternoon; So that the Top of the Stile points now upwards, as may be seen by Scheme 9th, and by the upper part of Scheme 10th. to wit, by the Semi Circle PTC; there∣fore when you chuse a Center in your design'd or real Plane for this Dial, let it be in the lower part of it to have Room for the Hour Lines to run upwards.

And by the way you must here remember, that tho' I bad* 1.1 you in the making of this your Vretical South Dial, to take the distance between the Zenith and the Intersection of the String with the next Hour Circle for the 1 and 11 a Clock Hour Lines, &c, yet that Section of your Globe by your String from the Zenith as aforesaid, gives in truth a North Dial, and therefore in strictness you ought to have taken the Distance between the

Nadir and the several Intersections of the Plane with the Hour-Circles; but since both Dials are (as I told you) alike, 'tis best always to operate thus from the Zenith, as being more at hand than the Nadir, and consequently more conve∣nient.

The Demonstration or reason why these Dials show the* 1.2 Hour, differs even at first Conception but little, and at the second not at all from that already given for the Horizon∣tal Dial. By the first Conception I mean our considering these Planes as Vertical and Erect; for since, the Hour-lines of all Dials are (as I show'd you in the former Demonstrati∣on) the Intersections only of the respective Hour-Circles with the Planes, and since the hourly indicating Shade, is the Shade of the Axis or of the Hour-Circle, which then lies in the Plane of the Sun, it must follow, that the Mark made (for example sake) by the 4 a Clock Morning Hour Circle on the String, and the Center of the said Plane (which is the common passage of all the Hour-Circles) will be two true Marks or Points for you to draw that hour-Line by, and consequently that the Shade of the Axis will still fall on the said hour-line as often as the Sun comes into the Plane of that Hour-Circle. Now your blind Circle is (by construction) equal to the Circle made by the String on the Globe, and the Marks on its Limb are equal to the Marks on the said String, therefore the Dial must be truly drawn, and the Stile plac't on the 12 a Clock line (to wit on the intersection of that Hour-Circle, which falls on the Plane at right Angles) must truly cast its shade from time to time, seeing by its Site and Angle it corresponds with the Axis of the World. As for our second Conception in re∣ference to these Dials, we shall find by it that their Planes are real Horizontal ones to some People or other; for this Section of the Globe being a great Circle will be the Horizon to those that live in the Pole of it, viz. to those under our Meridian 90 Degrees from our Zenith, which being a point in our Horizon, makes their Horizontal Dials always our Direct Vertical ones, and their Direct Vertical Dials our Horizontal ones. 'Tis plain then, that the present Dials are exactly describ'd, if our for∣mer Directions and Proof of an Horizontal one be true; for all the Hour Lines are here drawn from the Center to the several intersections of the Hour-Circles and Horizon, which (as we

are to suppose) the String represents. Nor do's the Cock of these Dials differ from the former Rules; for having the Meri∣dian or 12 a Clock line for Substilar for the former reason, and being 38 Degrees and a half above it, it makes an Angle equal to the Elevation of the People, who have the said Plane for Horizon.

Notes

• * 1.1

  A Memoran∣dum.
• * 1.2

  Demonstrati∣on.