GB2193351A - Adjustable sundial - Google Patents

Abstract

A Sundial consists of two semi circular arms 1, 4, fixed together at right angles and mounted by a cradle on a base. Adjustments for its location, for horizontal or vertical mounting and for use in either hemisphere are by movement of arm 1 aligning markings 3 against an arrow mark 11 on cradle 10. Arm 1 is reversible in cradle 10. Adjustments for longitude of location, for Equation of Time and for Summer Time are all made by markings 7 on strip 6 moving laterally against arrow marks 5 on arm 4. <IMAGE>

Description

SPECIFICATION Universal adjustable sundial This invention relates to a Universal Adjustable Sundial.

A Sundial only registers the local time at its actual iocation, that is, its latitude and its longitude. For civil purposes however, it is necessary to have one fixed time over a whole country, region or time zone. The unit used for this is the hour which represents the time taken by the earth for one rotation on its axis measured over a period of one year, and divided into twenty four equal parts. In Great Britain time was based on the Greenwich Observatory which lies on the 0 meridian and was called Greenwhich Mean Time (G..M.T.) Countries world wide now base their times on this and it is now known as Universal Time (U.T.) There is however another factor which must be considered.Due to changes in orbital velocities round the sun, the earth periodically reaches meridian by as much as 14a minutes before G.M.T. or as much as 164 minutes later. The times and dates are tabulated in The Equation of Time. They are constant for every year. Man-made Summer Time should also be catered for, twice yearly.

Accordingly, this sundial is so designed for universal use and is adjustable for: The difference in its latitude so that the gnomon can be aligned with the earth's axis.

The difference in its longitude with that of the meridian on which is based Universal Time in any country, region or time zone.

For being reversible according to the hemisphere in which it is located.

For correction to accord with The Equation of Time.

For its ability to be mounted horizontaily or vertically.

For its ability to deal with Summer Time.

In the accompanying drawings.

Figure 1 shows the Sundial in perspective.

Figure 2 shows the latitude arm laid flat (not to scale).

Figure 3 shows the hour arm and strip laid flat (not to scale).

Figure 4 shows the base plate and cradle (not to scale).

Referring to the drawings, Fig. 1 shows the Sundial in perspective but omits some of the markings at the ends of each arm. The semi circular latitude arm 1 has a fine wire gnomon 2 stretched across its diameter and positioned at the radius point of the arc formed by the -semi circular hour arm 4 on which its shadow will be cast.

Fig. 2 shows the latitude arm 1 laid flat. On its inner face, markings 0 to 90" on the upper segment are for use when the sundiai is mounted vertically and similarly 0 to 90" on the lower segment when the sundial is mounted horizontally. These markings 3 are for adjustment against an arrow mark 11 on the cradle 10 for the required latitude. This adjustment has the effect of aligning the gnomon 2 with the earth's axis.

Fig. 3 shows the semi circular hour arm 4 laid flat. It has a strip 6 of synthetic material lying in a shallow channel along its inner face which will have markings 7 for the hours and quarters and for a portion along its upper edge for degrees of the compass. For the Northern Hemisphere, the hours will run from left to right and a second strip will have them running from right to left for use in the Southern Hemisphere. This strip will be adjusted by lateral movement against arrow marks 5 on the shoulders of the hour arm 4 for correct longitude, Equation of time and Summer Time.

Two clamps 8 hold the strip 6 firmly after adjustment.

Fig. 4 shows the base 9 with the letters N and S inscribed on either end of a line on which is fixed cradle 10 having on it arrow marks 11. The latitude arm 1 sits in this cradle 10 with the gnomon 2 inclined northwards for use in the Northern Hemisphere or is reversed with the gnomon inclined southwards for use in the Southern Hemisphere. After adjustment against arrow marks 11 for latitude grub screws 12 are tightened to hold the arm firmly.

The two arms 1 and 4 are fixed together at right angles at their centres, the hour arm 4 standing proud, as shown in Fig. 1.

All adjustments on the sundial can be made prior to its being mounted in its permanent position, as follows: Using the appropriate segment for either horizontal or vertical fixing and inclining arm 1 for either use in Northern Hemisphere or Southern Hemisphere, adjust the latitude number mark 3 against the arrows marks 11 on cradle 10. Using the appropriate strip 6 for either Northern Hemisphere or Southern Hemisphere, place it in the channel of the hour arm 4 with the noon marking at the arrow marks 5 and then adjust it by lateral movement one degree for each one degree of difference between the longitude of the Sundial's position and that of the meridian on which the Universal Time is based (e.g. Greenwich Meridian 0 in Great Britain).This adjustment is by lateral movement towards the right for those positions lying to the east of the meridian: and towards the left for those positions lying to the west of the meridian. This adjustment for the correct longitude of Sundial must always be made irrespective of further adjustments which may be added to it or subtracted from it. These can comprise of The various times tabulated in the Equation of Time, adjusting strip 6 by one degree for each four minutes on the stated dates.

On four days in the year April 16, June 15 September 2 and December 26 the variation is nil and the intervals between alternate by adding or subtracting the times.

Adjustment for Summer Time by moving strip 6 fifteen degrees to the left in the Northern Hemisphere or fifteen degrees to the right in the Southern Hemisphere.

For mounting the Sundial in a vertical position, a South facing wall will be used and the letter N on base 9 will be uppermost while in the Southern Hemisphere, a north facing wall will be used and the letter S on base 9 will be uppermost.

Claims (8)

1. This Sundial can show Universal Time or Summer Time world wide, being adjustable for the latitude and longitude of its location; for variations of the Equation of Time; for man-made Summer Time; for being reversible for use in either hemisphere; and for mounting in either a horizontal or vertical position.

2. As stated in Claim 1, the adjustments for latitude to align the gnomon with that of the earth's axis and for choice of horizontal or vertical mdunting are made by the markings 3 on the appropriate segment of arm 1 against the arrow mark 11 on cradle 10. For use in either hemisphere the arm 1 is reversible in cradle 10.

3. As stated in Claim 1, the adjustments for the difference in longitude of the Sundial and that of the meridean on which Universal Time is based; for the variations of the Equation of Time; and for man-made Summer Time are all made by the lateral movement of strip 6 against the arrow mark 5 on arm 4 in which it is positioned.

Amendments to the claims have been filed as follows CLAIMS 1. A sundial comprising a base, a semi-circular latitude arm movably fixed within the base, the latitude arm being substantially semi-circular and having a gnomon extending across its diameter, a part-circlar hour arm adjustably fixed on said latitude arm, the centre of the circle defined by said hour arm coinciding with the axis of the gnomon, the latitude arm and the hour arm being provided with scale markings to permit adjustment of the sundial for the latitude and longitude of its location, for variations in the equations of time and for summer time.

2. A sundial as claimed in Claim 1, wherein the latitude arm carries a scale representative of the latitude of location, of the sundial.

3. A sundial in either preceding claim, wherein the hour arm is provided with a scale which indicates the time of day, being the shadow cast on the scale by the gnomon.

4. A sundial as claimed in Claim 3, wherein the hour arm includes a strip of synthetic material received in a shallow channel formed on the inner face of the hour arm.

5. A sundial as claimed in any preceding claim, wherein the latitude arm is fixed within a channel formed within the base by means of grub screws.

6. A sundial as claimed in any preceding claim, wherein the latitude ar is reversible to permit the sundial to be used in either hemisphere.

7. A sundial as claimed in any preceding claim, wherein the sundial may be mounted in either horizontal or vertical position.

8. A sundial substantially as hereinbefore described with referenCe to the accompanying drawings.