US157586A - Improvement im sum-dials - Google Patents

Description

Jj bavure.

Sun-Dials..

. Patented De,.8,1874.

UNITED STATES PATENT OFFICE.

JoHN DEvLiN, 0E rHILADELPHIA, PENNSYLVANIA.

IMPRQVEMENT sua-DIALS.

Specification forming partof Letters Patent No. 157,586, dated December 8, 1874.; application filed August l1, 1874.

simple and inexpensive automatically-actingA instrument whereby the meridian time and the degree from which to compute latitudev of the locality of the device will, without lifting or handling the same, be distinctly and accurately shown by the shadow of a magnetic needle poised horizontally upon a vertical support fixed in the apex of a hemisphere, marked by a series of equidistant latitudinal lines from base to apex, and the lines and intermediate spaces divided and numbered on a longitudinal line, to indicate degrees from l to 90, as will be more clearly explained, with reference to the accompanying drawings, in which- Figure 1 is a perspective view of my said indicator, secured upon a circular platform and covered by a glass shade. Fig. 2 is a plan View of Fig. l. Fig. 3 is a side view of the magnetic needle, enlarged.

'lhe hemisphere A is made of wood, or any other suitable material, and is circumscribed by latitudinal lines at equal distances apart, and commencing at its base, thus dividing its surface from base to apex into nine equal parts, which are numbered from 10 to 90, inclusive, from the first line above its base to its apex, along a longitudinal line, a', which is marked by a series of short horizontal lines, dividing each space between the latitudinal lines into five equal parts, each indicating two degrees. The magnetic needle B is a straight bar of steel, about twice as wide as it is thick, and one-fifth longer than the diameter of the hemisphere A. It has a conical cavity in the mid-length of its lower edge, which extends nearly to the opposite or upper edge, whereby it is supported edgewise and horizontally, so as to swing freely upon the. point of the vertical pole or stem C, at a short distance above the apex of the hemisphere A, as represented in Fig. l. The indicating end of the magnetic bar B has a short slender' bar of steel, b', fixed at right angles to the sides of said bar, so as to project from each side to the length of about one-eighth of the length of said magnetic bar B, and is secured in position by `means of a small binding-screw, bo, in the said end of B. The opposite end of B is slotted to receive an adjusting-screw, b, provided with a head, and adapted to be readily screwed inward and outward in bringing the needle B into equipoise, or true horizontal position, upon its support C. The bottomof the hearinghole in the mid-length of B is intended to be jeweled, in order to reduce friction as much as possible, that the magnetic needle may 'come to thegnorth and south directions with facility.

The proportions of the different parts of my said invention should be as follows, viz: lf the diameter of the hemisphere A be live inches, the length of C should be one-eighth of an inch for each inch of said diameter of A, and the length of the magnetic needle B onefifth longer than said diameter, or six inches, and the length ofthe cross-bar b about onefourth of that of the magnetic needle B. These proportional lengths are for all sizes of the hemisphere; and the larger the same may be, the moredistinct and observable will be the indications.

The device shown in the drawings is specially adapted for the northern hemisphere of the earth only. For the southern hemisphere, the opposite end of the magnetic needle B must be fitted with the cross-bar b', and the longitudinal line of degrees a also made on the opposite side of the hemisphere, or the said hemisphere rotated half-way around, because the rays of the sun will come from the opposite direction in this case.

When the invention is to be used in both hemispheres, it is intended to have both ends of B provided with a cross-bar, b', and the hemisphere A with two like lon gitudinall scales,

In using 'my said device or apparatus, it must be placed so as to rest with the base of the hemisphere A in a true horizontal plane, and with the longitudinal line of the scale a coincident with the north and south direction of the magnetic needle B when the latter is at rest in its proper horizontal position, as represented in Figs. l and 2. Now, when meridian time arrives, the shadow of the indicating end of the magnetic needle B will correspond precisely with the longitudinal line of the scale a', and the two ends of the curved shadow of the cross-bar b will be at the degree-line corresponding with the altitude or declination ofv the sun, and thus the true degree for computing therefrom the latitude of the place of observation.

The shadow of the magnetic bar B on the hemisphere A from the vernal equinox, March 20, descends on said. hemisphere one degree for each degree the earth moves its pole toward the sunabout twenty-three degrees to June .2lwhich gives seventeen degrees latitude from the celestial equator. The shadow now returns with the earth, and in ninety-two days gets to the autumnal equinox, September 21 or 22; and when the earth has moved its pole its greatest distance, December 21, the shadow of the said magnetic bar will be about at sixty-three degrees from the equator, or twenty-seven degrees polar distance. From the equinoctial degree of latitude either way (north or south) there are ninety-two days, nearly. Now, as four days give one degree declination, ninety-two days divided by four equal twenty-three degrees; and as one day is equal to one minute of time, so is four days to a degree of declination, and one day or minute seventeen and one-fourth miles, which,

multiplied by four, gives sixty-nine miles to one degree.

Refraction ofthe suns rays by the glass cover is not appreciable in observing the shadow of the magnetic bar or needle B; but, as it is intended merely as a protective cover, it may be simply lifted off before taking the meridian time and latitude, if it be desirable.

For use at sea, the whole apparatus is in tended to be suspended by gimbal-rings, in the same manner as a marine compass.

I claim as my inventionl. The automatic indicator, consisting of the hemisphere A, provided with the series of latitudinal lines and the longitudinal scale of degrees, and also with the vertically-projecting stem C, as set forth, in combination with a magnetic bar, B, balanced and swinging freely upon the top of said vertical stem C, in the manner and for the purpose hereinbefore described.

2. The adjusting-screw b, in combination with the slotted or recessed `end of the magnetic bar B, substantially as and for the purpose herei-nbefore set forth and described.

' JOHN DEVLIN.

Witnesses:

BENJ. MoRIsoN, WM. H. MonIsoN.

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