US1570029A - Sun dial - Google Patents

Description

S. W. BALCH Jan. 19 1926.

SUN DIAL Filed April. 18. 1922 3 Sheetsheet 2 rwentor,

Patented Jan. 19, 1926.

UNITED STATES SAMUEL W. BALCH, OF MONTCLAIR, NEW JERSEY.

SUN DIAL.

Application filed April 18, 1922. Serial N'o. 554,648.

To all fio/tom t may concern Be it known that I, SAMUEL lV. BALCH, a citizen of the United States ot America, and a resident of Montclair, in the county of Essex and State of New Jersey, have invented certain new and useful improvements in Sun Dials, of which the Jfollowing is a specification.

The object of this invention is to provide a sun-dial which will indicate standard mean time on any day between seven in the morning and live in the afternoon when the suns rays can reach the dial, and with a degree of accuracy which is limited only by the closeness with which the shadow can be determined, and which will also indicate the time with small error before and. after this period of the,- day. A further object is to provide a sun-dial which can be adjusted for any latitude and for any time meridian, the time of which may be used in the place `where the sun-dial is located instead of the local time. A further object is to provide a sun-trial which while accurately indicating mean time, can be permanently adjusted when set up and requires no further altera-- tion for dii'lerent times of the year and which shows the true mean time directly and without requiring recourse to tables and calculation.

In the accompanying three sheets of drawings which form a part ot this specification- Figure l is an elevation of a sun-dial embodying this invention, looking north.

Fig. 2 is an elevation of the same, looking west, the eyes being shown in section.

Fig. 3 is an elevation of the gnomon, looking east.

Fig. 4t is a plan oi' the gnomon drawn to three times the scale of the preceding {ig-I ures.

Figs. 5 and 6 are sections through the gnomon on the lines V-V and VI-/ I respectively to the same scale as Fig. 4.

Figs. 7 and 8 are similar sections of a chining a cylindrical seat on the wings. A circular arc ,f with time graduations is tastened to the wings and the arms support the ends or' a gnomon with positive and negative sides g and g respectively. The main frame is supported `from a base 71. which' clamps the frame in any required adjustnient for latitude. There is an upstanding tongue z' on which one of the arms ot the frame rests. The tongue is slightly narrower than the arms and jaws j, j are drawn together by a bolt 7^: to clamp the frame.

Sun time varies from mean time throughout the year. The sun is on the meridian later than twelve by the clock from J une l5 until September l, and also from December 25 until April l5, and is on the meridian earlier than twelve by the clock during the two remaining periods oi the year. These times are given in almanacs under the heading Sun on the meridian. As the sun changes from day to day in declination, a diiferent part of the gnomon casts its shadow across the time scale on each successive day, and it is therefore possible by using a gnomon of suitable form to displace the shadow on each day by the amount of correction required. By making the dial scale a part of a circle whose axis is parallel to the earths axis and the gnomon a solid of revolution about this axis and ot proper form either the positive or the negative corrections can be accurately made 'for all times 0i' the day when the suns rays can reach the dial, but not both. This is because it so happens that the sun is at each particular declination on two different days of the year, on one of which the correction is usually positive and on the other of which it is negative. As these are also usually ot slightly different numerical values such a gnomon cannot be accurately shaped for all hours of both days. By restricting the surface of revolution to between l5() to 180 degrees the period of accurate marking on each day will be limited to from ten to twelve hours, and this is not objectionable as the interval during which a sharp shadow is cast is usually within this period. As the arefor the negative correction is on the opposite side of the gnomon from the arc for the positive correction both can be at the same declination part of the gnomon without materially interfering.

The curve of the gnomon is found by iirst drawing a curve on which each day is represented by a point the abeisaa ol which is the sine ol the equation ot time and the ordinato ot which is the tangent of the cuirs declination le the sharp edge of the 'shadow ia 'where the Aumbra joins the penumbra and not at the middle of' the penumbra7 the sun`s semidiame'ter is laid off normal to this curve, and the true curve is calculated by mali: .if the absissa equal to the sine ot the equation ol*l time plus the product o11 the :limb` semidiameter .multiplied by the iiccant oit' `the :slope oi the gnomon. On ,lune 2l and December 2Q the shadow is cast by the tipa ot the gijnomon. and in calculating' the position of these tips, the suns seniidiameter is added to the declination in stead ot to the equation of time. The sines and tanirgents4 are the dimensions of the gnomon on the basis et a scale according' to which unity is the radius of the are bearing the time graduations. Each function must be multiplied by the radius it' any other length than unity is used; In the following` table there is shown for selected dates the equation et time e, the suns semidianieter Ks', the correction for the slope ot' the gnomon c, the suns declination (Z, and the coordinates fc, 1/ computed therefrom.

In the rase ol each pair of dates of nearly the Same declination the average ordinate is u scd 'for simplicity Without introducing material error.

The equation ol time is usually given in alinanacs in minutes` and seconds ot time. The numerical value4 are niultiplied by l5 lo convert to minutes and seconds ot arc a iirrn in the above table. A preliminary curro ia iirat drawn an lShown in dotted lino in lil' i) without int-rmlucinfbi` the correction ier thc :ams l emidianieier. In this preliminary curve lhe absiesre are the since ol the equatioi'i oll time and the ordinates arc the tangente ol the euna declination for the Same imstanis ol' time. l"roin this carre the Slope ol thc gnomon at each point is measured, and the suns scinidiameter is corrected by multiplyingir by tlie riet-ant ol,h the angle ot1 the slope. Thus at l`)c ,',e1nbcr 3l the slope is found by measurement to be 50 30 and the suns sclnidiaineter, 113 18" multiplied by the secant yis 25 213, an increase of D 20 as shown in column c of the table. The absissa for this date is the .sine ol' the sum oi the anglel `in the three columns c, t, and c, oi'ipoaite the date.

A modilication ot the `gnoinon is Shown in Figs. '7 and 8 by which it is made a single surface oi revolution and .its construction thereby sinipliicd. At each point ot declination ita diameter is the numerical sum of the positive and negative absissze. It would need to be set With its axis deviat4 ing titty minutes of are from the true north and south axis. the north end being to the east and thc south end to the west.

Ars; the gnomon casts a shadow With two edges crofersinpr the line ol time graduations, oli which only one indicates the mean time, it is necessary to show from which edge the time is to be read. The names of the months are therefore linscribed on the Sides of the gnomon. It is only necessary to touch ones finger to the month and its shadow will point to the side from which the time is to be read.

l. In a sun-dial for indicating mean time, a dial bearing a circular are with time graduations, and a gnomon shaped so that every day shall be rcprc'cnted by a point on the surface the absk 'a ot which measured from the axis: ot the circular arcI is the eine ot the aum o1 the equation ol time and the product of the .sunk sc1nidiameter with the Secant ol the slope at the point with respect to the axis ol. the circular arc, and the ordinate ot which nfieasurcd from the plane of the circular arc if the tangent ot the suns declination.

2. In a sun-dial tor indicating mean time, a dial bearing a circular are with time graduatione, and a gnomon in which racli of the two sides i5 bounded by approximately half o'l' a surface ot revolution about the axis ot the circular arc. the tiro sides being dissimilar. one sido bcinpr ligurcd lor the pofiitive corrcrtioia; lo sun time and the other ltide bciniiA figured l'or the negative corrcctiona to aan (imc.

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