Sun clock
BACKGROUND OF THE INVENTION 
     The present invention relates to the art of indicating time using the position of the sun and more particularly to an improved method and means for producing an indication of solar time using the contrast between an illuminated line, formed by sunlight passing through a flat slotted opaque surface, and a darker background on another flat surface. 
     Horological devices using the position of the sun in the sky have been known since ancient times and have generally involved some means for casting a shadow whose position on a scale provides an indication of the time. Various instruments for this purpose have taken many forms from the simple sundial with its triangular shadow casting member disposed on a circular time-indexed base to more structurally complicated and sophisticated solar clocks such as disclosed in U.S. Pat. No. 3,486,234 to Waterman and U.S. Pat. No. 3,786,570 to Davies. 
     The present invention presents a simplified method and means for indicating solar time incorporated in a box-like sun clock which may be constructed in various forms to present an illuminated line on a darker background time indication for viewing both indoors and outdoors. 
     SUMMARY OF THE INVENTION 
     The present invention embodies a method and means by which solar time can be determined through the imaging of an illuminated line of sunlight on a flat darker background. The sunlight is passed through a slot in a flat opaque member and imaged on a flat time-indicating member, which members are appropriately oriented with respect to each other and to latitute and the earth&#39;s &#34;true&#34; north/south axis. The slotted opaque member which may constitute one face of a rectangular box-like structure is disposed with respect to the sun at an angle corresponding to the latitude at which the clock is to be used, and the long axis of the box, or the short axis of the slot, is arranged perpendicular to the earth&#39;s &#34;true&#34; north/south axis. The sunlight passing through the slot is imaged as an illuminated line on the time-indicated member, which may have a translucent time index thereon and be the opposite box face parallel to the opaque member or an adjacent side face. Alternatively the time-indicating member may be disposed centrally in the box perpendicular to the opaque member and bisecting the slot. In the latter embodiment at least one adjacent side face of the box is omitted to permit viewing of the time-indicating member. In all the embodiments suitable support frames or stands may be used to mount the box in the proper position, and in certain embodiments the stand may also act as a sun shade. The position or size of the illuminated line may be used to indicate time, and a number of structural variations and features are disclosed within the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective exploded view of one embodiment of a sun clock and a supporting stand in accordance with the present invention. 
     FIG. 2 is a diagrammatic view of the sun clock of FIG. 1 illustrating time index calibration for clocks of different proportions. 
     FIG. 3 is a perspective view of an alternate embodiment of a sun clock in accordance with the present invention. 
     FIG. 4 is a perspective view of the sun clock of FIG. 3 mounted on an appropriate support frame. 
     FIG. 5 is an elevational view of a sun clock of the type shown in FIG. 4 with the support frame modified for adjustability. 
     FIG. 6 is a view as in FIG. 5 showing the position of the clock adjusted for a different latitude and high and low angles of the sun. 
     FIG. 7 is a view as in FIG. 4 illustrating a modification of the sun clock shown therein. 
     FIG. 8 is a view as in FIG. 5 showing the modified sun clock of FIG. 7 in a summer orientation. 
     FIG. 9 is a view as in FIG. 5 showing a further modification of the sun clock of FIG. 7 in a winter orientation. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One embodiment of sun clock in accordance with the present invention is shown in FIG. 1 and essentially comprises an elongated rectangular member or box 1, one of whose side faces 1a is opaque and provided with a centrally arranged slot 2. The box face 1b, disposed opposite face 1a, is translucent or has a translucent, proportionally expanded linear time index 3 formed thereon. The index or scale 3 is formed or calibrated in the manner of a polar sun dial as will be familiar to those skilled in the art and as explained, for example, in &#34;Sundials&#39; Their Theory and Construction,&#34; Chapter 9, pages 70-74, by Albert E. Waugh, Dover Publications, Inc., New York, 1973. 
     In operation, the parallel faces 1a and 1b are tilted at the angle of latitude of the site where the clock is to be used with slot 2 facing the sun, and the long axis of the box 1 is disposed perpendicular to the earth&#39;s &#34;true&#34; north/south axis. With the box 1 in this position the leading edge of the light image or line I formed by the sun&#39;s rays R passing through the slot 2 will indicate solar time along the time index 3. It will be seen that in comparison to known sun dials or clocks, the time will be indicated by an illuminated line on a flat darkened scale background. 
     An appropriate manner of disposing the sun clock at the proper orientation with regard to latitude and the earth&#39;s axis is by means of a support frame 4 in the form of a base member of flat stand 4a having upstanding end members 4b and 4c. As seen in FIG. 1, the end members 4b and 4c have their upper edges suitably cutout or bevelled to receive the end edges of box-like member 1. The surfaces of the cutout portions engaging the scale or display face 1b of box-like member 1 are arranged at an angle with the plane of the stand 4a corresponding to the appropriate angle of latitude at which the sun clock is to be used. If the clock scale 3 is to be viewed at or below eye level, a mirror 5 may be mounted on the support frame 4 adjacent and at an angle to the scale face 1b to reflect the time index therefrom. In such event the numerical indications on the time index 3 may be appropriately reversed as shown in the figure. 
     The box-like member 1 and support frame 4 may be constructed of a light plastic and, except for the slotted face 1a and the scale face 1b, the faces or parts may be either translucent or opaque. In addition to the time index lines on face 1b, hour lines 3a may be marked along the path of the rays on the other side faces and the end faces as well, in the manner shown in FIG. 2. It will also be seen with reference to FIG. 2 that the proportions of the box-like member 1 may be varied as desired but will require altering of the position of the hour lines on the appropriate faces. As illustrated in the figure, the time index on the various faces is determined by graphically extending rays every 15° from the edges of the slot 2. Where the graphic rays intersect the faces, such as display face 1b, the hour lines 3a are located. Subdivisions of the hours can be located on the index using the same method and subdividing the angles of the graphic rays. If every side of the box-like member 1 with the exception of the face 1a is made of translucent material, hour markings can be placed on five sides of the sun clock. Such an arrangement would permit reading of the clock from many directions. 
     In any event, irrespective of the materials and proportions, with this simple clock, as the sun moves across the sky, the slot will form a light image or line I at least on the translucent scale or display face 1b, the position of whose leading edge along the proportionately expanded numerical index 3 will accurately indicte solar time. The clock is suitable for use both indoors and outdoors. 
     An alternate embodiment of the sun clock of the present invention is shown in FIG. 3. In this embodiment the box-like member is modified by relocating the translucent-scale-containing face. More particularly, box-like member 10 has an opaque face 10a with an appropriate central slot 20 and the side faces adjacent face 10a are removed. A translucent-scale-containing face or display face 10b is centrally disposed within the box-like member 10 perpendicular to the slotted face 10a. In this instance a radial pattern of hour lines 30 is formed on the display face and the lines are arranged at the same angle as the graphic rays used in forming the linear scale in the first embodiment. Thus, the location of the hour markings on the display face with the present invention is a matter of choice, as they can be arranged as parallel lines as in the first embodiment, or radially as in this embodiment. In this embodiment the proportions of the clock have been altered to allow the inclusion of hour lines from 6 a.m. to 6 p.m. Parallel hour lines may also be marked on the bottom face 10c and end faces 10d and 10e and those faces made translucent. The slot 20 in opaque face 10a may be varied somewhat in configuration, while retaining its essential form with a long and a short axis, by pointing its opposite ends. As with the first embodiment, this alternate embodiment may be made in any suitable size and located both indoors and outdoors. 
     In operation, this embodiment is positioned in the same manner as the first embodiment to record solar time. As the sun moves across the sky, sun beams or rays of light will pass through the slot 20 and form an image I 0  on the display face 10b in the general form of the slot. This image rotates on the display face of the clock in accordance with the sun&#39;s movement. At a particular time the direction or angle of the ray image will coincide with a time line marked on the display face and will point to or illuminate the appropriate hour lines on the bottom or end face. As the day progresses, the changing width or shape of the beam image I 0  will provide a crude indication of the time as well, that is, the beam is widest at noon and narrowest at sunset or sunrise. It is contemplated that this changing width or shape of the beam image can be used with various calibrated mechanical or electronic systems to provide a time indication. As mentioned above, the proportions of the clock will be determinative of the appropriate scale proportions. 
     Provision may also be made for the seasonal variations in the sun&#39;s position. In particular, the beam image I 0  formed by the pointed slot 20 will vary throughout the year. During the winter months the sun is low in the sky, so that, as indicated in FIG. 5, sunlight entering the slot will intersect and backlight the display face 10b. In the summer months the sunlight will intersect the display face from the viewing side of the clock. At the time of the equinox on or about March 21 and September 23, the sun will enter the slot parallel to the display face, and, as a result, the face will remain unlit with only the bottom and end faces receiving light, so that the clock can thusly be used to signal the equinox. 
     The hour markings 30 on the relocated display face in this embodiment allow the display face 10b to be viewed without the assistance of a mirror as in the first embodiment. However, this relocation of the display face requires a further provision with this embodiment. Between March 21 and September 23 the sun rises north of each and sets north of west in the northern latitudes, so that during these months the sun will enter a properly positioned clock through the open viewing face as well as through the slot 20. This light is unwanted as it will obscure the sharp delineation of the bright beam image on the darker display face. Consequently, a sun shade may be provided whose primary function is to shade the clock face from low oblique sun rays during the early morning and late afternoon hours. Conveniently, the sun shade may be constructed as part of an adjustable stand for the clock and may be of a form such as support frame 60 in FIG. 4. The support frame 60 consists of an upper sun shade face 60a with upstanding support members 60b and 60c attached to its opposite ends. The box-like member 10 is disposed within the frame with the upper edge of the open viewing face abutting or attached to the rear edge of the sun shade face 60a and with the end faces 10d and 10e abutting or attached to the upstanding members 60b and 60c. The members 60b and 60c may be translucent to permit viewing of the display face through a wide range of angles, even though during a few weeks of the year around June 21 the early morning and late afternoon sunlight will pass through these members onto the display face. However, that amount of light will not obscure the sharp delineation of the beam image on the display face. 
     As shown in FIGS. 5 and 6 box-like member 10 may be adjustably mounted on the support frame 60 by the use of a suitable hinge 61 which connects the upper edge of the slotted face 10a and the rear edge of the sun shade face 70a and by providing appropriate arcuate slots 62 in the upstanding members of the frame, which slots accommodate appropriate pin members 63 on the end faces of the box-like member. Appropriate stop means in the form, for example, of set screws may cooperate with the pin members 63 to set the box-like member 10 at the appropriate angle. Indoors a shading means will not be necessary, and the clock can be situated on an open stand similar to that used with the first embodiment. 
     A further embodiment of the present invention modified to somewhat combine features of the two previous embodiments is shown in FIGS. 7-9. It will be seen that in this embodiment the centrally-located indicator face may be disposed on either edge of the box to accommodate it for use in different seasons. For example, from September through March the face 10&#39;b is placed toward the viewing side (FIG. 9) so that it is backlighted by the winter sun, while for the remainder of the year the face is located on the opposite side and frontlighted by the summer sun (FIG. 8). This change provides a suitable accommodation for the seasonal variations as described in connection with FIGS. 5 and 6. To this end the indicator face 10&#39;b of the clock is adapted to be detachable such as by providing slots in one or both of the end faces of the box 10&#39; through which the indicator face 10&#39;b may be inserted and removed. This arrangement can perhaps be more clearly seen in FIG. 1 wherein a slot 1z is provided in face 1e to permit the insertion and removal of appropriate time index panels. In this manner, different display faces can be interchanged when desired to provide for different time changes such as daylight savings time and for different decorative patterns according to the season. Essentially in this embodiment it will be seen that the depth of the box as compared to that shown in FIG. 4 is reduced and grooves may be formed on the bottom and top faces to guide the display faces when being slid in and out of position. 
     An additional modification which may be included in any of the embodiments is the use of an insert piece 20&#39; in the form of a bicolored rectangle of transparent plastic that fits into the slot of the various clock embodiments. This piece 20&#39; will result in the projection of a bicolored beam from the light passing through the slot, with the border between the two colors of the beam bisecting the slot longitudinally forming a precise time indication. 
     It will be seen by those skilled in the art that the present invention will provide an indication of solar time both indoors and outdoors the year round unlike many prior art devices such as the typical indoor sun dial disclosed in the early U.S. Pat. No. 783,245 to Clarke wherein between the dates of March 21 and September 23 the sun would at times be inclined at such an angle that the line cast by the shadow cord would not always reach the display surface. 
     The term &#34;translucent&#34; as used herein is intended to refer to any structure which will pass light whether in an unobstructed manner as by voids, transparency or the like, or by reflection, refraction, or diffraction as long as some representation is presented to view on the opposite side of the structure from which the light is impinging.