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 XXIX. To make a Dial by which a Blind man may constantly know the Hour.

YOU must first get made in Brass the Armillary Hemis∣phere* 1.1 ABCDE (as in Scheme 35) 8 Inches, suppose in Diameter, representing your Globe cut throu' the Horizon; but the said Hemisphere is not to have any thing solid remaining, besides the Horizon ABCE with the Pieces of the Hour Cir∣cles (1234, &c) that reach to it from the Nadir, or rather from the Tropic of Capricorn AFC on the Northernside, for the Southerly Circles are superfluous. Then having plac'd the said Hemisphere directly North and South, as your Globe stands when Compos'd, fix G a Glass Bowl of clear water 4 Inches in Diameter (i. e. half the former) in the midst or center of it; for the Sun's Beames passing throu' the Water will contract in a

Point, and ever burn at (suppose H) the true Hour-Circle; so that if a Blind-man puts but his Hand on the said Brazen Hour Circles, he will soon find by the Heat where the Sun marks, and consequently tell you the Hour; for he may easily feel how far it is from the middlemost Hour Circle, I mean the 12 a Clock Circle or Meridian.

As for the Reason of this Operation, 'tis presently con∣ceiv'd;* 1.2 for when the Sun is over against (suppose) the 5 a Clock Hour Circle on the South-side of the Dial, he must needs be over against the same Hour on the North∣side, both hours making but one Circle; Now since the Center of the Bowl (by being in the Center of the Hemi∣sphere) is in the Plane of all the Hour Circles, and since (according to the nature of Refraction) all Parallel Rays of the Sun, passing throu' a Sphere of Water, are (where they meet with the Direct Ray, that passes throu' the said Cen∣ter) contracted into a point, viz. on the opposite side, at the distance of half its Diameter, or two Inches according to our present Example; I say, seeing this, it must needs follow, that at 5 of the Clock, the Sun will burn on the correspond∣ing Hour-Circle, and if so, then a Blind-man (by feel∣ing the Heat, and finding its distance from 12) must needs be able to tell you the true time of the Day.

Notes

• * 1.1

  The constru∣ction.
• * 1.2

  The Demon∣stration.