GB2308900A - Polyhedral sundial - Google Patents

Abstract

A sundial is formed from a series of flat surfaces arranged helically. Time is indicated by the shadow cast by the sun on the series of surfaces. The surfaces are set around an axis parallel to the earth's axis and in such a way that by their angle of orientation to the sun, they will fall in or out of shadow at regular given intervals through the day.

Description

POLYHEDRAL HELICAL SUNDIAL This invention relates to a sundial.

Sundials are a well known means of time indication. The are usually based on an apparatus arranged to mark the shadow of the sun and thus read the time from the shadow's position.

The method usually used employs the rotation of the earth to change the orientation of the sundial to the sun, thus advancing the indicated time throughout the day.

A line or edge (the gnomon), running parallel to the earth's axis is commonly used to cast a shadow onto a surface on which time increments are indicated.

Less common but known are sundials in the form of a helix, where the axis of the helix runs parallel with the earths axis. Time can be indicated on the surfaces of the helix with it's own edge acting as a gnomon.

It is also known that a flat surface, orientated to run parallel to the earths axis, will fall from sun to shadow (or vice versa) at approximately the same time each day, and can be used as a time indicator.

By basing the principal of the sundial on the orientation of a series of surfaces rather than the orientation of a shadow thrown upon a scale, a novel, inexpensive garden sundial can be produced by a simple casting method.

According to the present invention there is provided a sundial comprising a polyhedron, that has a series of surfaces arranged on it to indicate time. The surfaces are arranged as a number of flat polygons, each one arranged to indicate a set time. The polygons may be marked with time interval indications. The polygons are arranged in a way that with the correct orientation of the polyhedron, time is indicated as the surfaces of the polygons move from shadow to light or vice versa.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 Shows an example of a four sided dial at 15 minute increments of time. Shadow indicates time of nearly two-thirty. Two-fifteen has passed as it is now in light, two-thirty is just coming into light, indicating a time nearing that point.

The axis A-A is parallel to the earths axis and the centre of rotation for the polygons.

Angle "L is the degrees of latitude north or south that the sundial is positioned with H-H as horizontal.

Figure 2 Shows a four sided dial at hourly increments. Time indicated between twelve o'clock and one o'clock. The pattern is repeated on the opposite side but will run from shade to light rather than from light to shade as indicated.

The last three/nine increment is repeated to clarify time at the changeover point from one face to the next.

Hours are marked on the faces. Time can be indicated as being between two points (the last face that is in sun and first face that is in shadow) or at one point if a face is just turning in or out of shade.

Figure 3 Shows the dial sides incorporated on a cylindrical shape with gaps between each side. Time scale is indicated next to the face. Each face can be seen to be 15 in rotation (= one hour) about the axis of the cylinder.

Latitude can be adjusted by the positioning of the base on the support arm.

Figure 4 Shows a single set of faces on a cone shape. The faces are separated from each other and inclined to the angle of latitude (Geometric working is left for illustration).

Figure 5 Shows two faces at fifteen minute increments, set into a solid block. Time indicated at nine o'clock to nine-fifteen. The sundial has "A at 45" so is set to work at a latitude of 450 north. The sundial would be orientated to be on the north-south N-S line indicated (in the northern hemisphere).

Considerable difference in the overall shape and character of the sundial will occur in varying latitudes. In the southern hemisphere, as with conventional sundials, the time scale markings and orientation will be in the opposite direction to the illustration.

Figure 6 Shows the sundial incorporated into a shell design. The dial is a six-sided inclined tapering shape.

Figure 7 Shows the geometric principal of the faces of the dial.

By way of an explanation of the timekeeping feature of the sundial, the properties of the dial is described.

A point on the earths surface rotates 360 (relative to the sun) over 24 hours. This is, for example, 15 rotation in one hour.

A flat surface set with an axis parallel to the earth's axis will rotate with the same properties as the earth, and will move in or out of sun's light at a regular time of day. The time can be altered by the surfaces orientation to the axis. Thus two surfaces both on the given axis, but orientated 15 apart can be used to indicate a time period of one hour.

This principal can then be repeated with any number of surfaces to indicate any time period or divisions over the day and can take the form of a helix shape, as the surfaces (faces), indicating a series of times, are set on the polyhedron. The time can then be read off the polyhedron as the sun's shadow moves up or down the scale of faces and each face in turn moves from shadow to sun or vice versa.

Each face is in the form of a polygon. The polygon edges can be of any form or shape but each polygon surface (F) must have the following geometric properties; (fig 7) a) Be parallel (P-P) to an axis (A-A) of the polyhedron.

b) Be at 90" to the axis and form (C-C) a chord or be parallel to a chord of a circle with a plane at 90" to the axis.

Each polygon can form the polyhedron at any point on its surface and be arranged in any way as long as the properties are maintained.

The leading edge of the polygon is that acting as a gnomon so the polygon can be of any shape.

The number of faces can be varied, depending on the time interval set between each face.

A 'side' refers to a series of faces that are incorporated on the polyhedron. Each side can indicate time over a segment or all of the day. The indicated time can follow-on, overlap or repeat from one side to the next. Any number of sides or faces can be used.

The sundial itself can take the form not only of a helix on a cylinder or cone, but as long as it maintains it's properties, can be set over or incorporated in any shape or form of polyhedron.

The polyhedron can take the form of another object and incorporate the sundial on part of the surface.

Designs can be incorporated between or around the sides and/or between or around the faces of the sundial.

With the particular character of this invention it is clear that all the variations in design, number and configuration of the sides and faces, and the character and shape of the polyhedron on which they are placed, can not be fully illustrated here.

Claims (3)

1 A sundial comprising a polyhedron, that has a series of surfaces arranged on it to indicate time. The surfaces are arranged as a number of flat polygons, each one arranged to indicate a set time. The polygons may be marked with time interval indications. The polygons are arranged in a way that with the correct orientation of the polyhedron, time is indicated as the surfaces of the polygons move from shadow to light or vice versa.

2 A sundial substantially as described herein with reference to Figures 1-7 of the accompanying drawing.

3 A sundial of any form using the principal of layout as described herein.