Geometrical instruments – Straight-line light ray type – Celestial
Reexamination Certificate
1999-08-23
2001-10-30
Hirshfeld, Andrew H. (Department: 2859)
Geometrical instruments
Straight-line light ray type
Celestial
C033S268000
Reexamination Certificate
active
06308427
ABSTRACT:
BACKGROUND
a. Field of Invention
This invention relates generally to horizontal sundials, and specifically to a method by which a horizontal sundial constructed to tell time at a specific latitude, is easily adjusted to accurately tell time at latitudes greater or lesser than the latitude for which it was constructed.
BACKGROUND
b. Description of Prior Art
Prior art in the construction of horizontal sundials has been focused on making a sundial designed and constructed for stationary use at a specific latitude. A horizontal sundial properly constructed to tell time at a specific latitude must meet certain design requirements. The gnomon or shadow casting portion will lie perpendicular to the dial plate on a line bisecting the dial plate and passing through the noon mark. The gnomon will make an angle with the horizon equal to the latitude at which the dial will be used. Hour marks will be layed out on the dial plate surface with spacing appropriate to the latitude. The elevated end of the gnomon is at the same end of the dial plate as the noon mark, which is considered as the north end, since the elevated tip of the gnomon points at the north star when properly aligned. No provision was made in the design of early dials for adjustment for use at any other latitude.
A method of adjusting a horizontal dial to read accurately at a latitude other than its design latitude has long been known. The appropriate adjustment depends on the original design latitude and the latitude of intended use. The adjustment consists of raising either the north or the south end of the dial with a wedge so as to adjust the angle of the gnomon to be equal to the latitude of use. This method has the drawback of requiring that a wedge be made with considerable accuracy. It is unlikely that accuracy of better than one half degree can be achieved using generally available tools and having normal skill. It also would require a reasonable time expenditure. This is not something easily accomplished by everyone. This method also only allows for a single latitude adjustment. It does not have the flexibility of a continuum of possible adjustments.
A variety of means have been used to adjust dial plates for latitude of use. U.S. Pat. No. 825,319 to Hewitt (1906) uses screws as part of a pivoting mechanism used to adjust the dial plate to the latitude of use. The screws are set screws used to secure the gnomon angle at the angle corresponding to the latitude. These screws play no role in finding or determining the angle appropriate to the latitude. Methods used to find the correct gnomon angle are visual sightings at night and measuring the angle the gnomon makes with the horizon. These methods are crude, lacking accuracy, and not easily implemented.
In U.S. Pat. No. 1,146,412 to Early (1915), a complicated mechanism involving a quadrant or protractor scale on a pivot, a pointer or indicator, and an adjusting screw as part of a more complex mechanism is used to tell time. The function of the adjusting screw is to achieve a more exact positioning of the dial plate relative to the indicator showing the angle of use. This is a complex mechanism, external to, but connected with, the dial plate. The adjusting screw is a set screw since the adjustment to the angle indicated on the quadrant scale is visual. Accuracy is only as good as the divisions on the scale allow. Such a mechanism including the necessary supporting stand is expensive and unnecessarily complex.
In U.S. Pat. No. 4,103,429 to Wagoner (1978), a protractor incorporating a clamping screw is also used for latitude adjustment. This instrument is quite complex in both its construction and in the means necessary for its accurate use. In this case as with many other devices regarded as sundials, their design makes them virtually unrecognizable as sundials to the average person. Almost no one would consider mounting them in a garden, since their design results in a lack of aesthetic appeal.
Prior art has not achieved the ideal of a means of constructing a horizontal sundial which is inexpensive to manufacture, can be adjusted to operate very simply at any latitude, and which is very accurate when properly adjusted and aesthetically pleasing.
OBJECTS AND ADVANTAGES
Accordingly, the objects and advantages of the present invention are:
(a) To provide a horizontal sundial which can be adjusted simply to latitudes either greater or lesser than the latitude for which it was designed.
(b) To provide a design that is inexpensive to manufacture.
(c) To provide a method of adjustment to the desired latitude with great accuracy.
(d) To provide a design that does not alter the appearance of a horizontal sundial in a manner that makes it aesthetically unattractive
(e) To provide a design that does not require a protractor or any direct means for reading or determining the gnomon angle, while allowing the desired angle to be achieved with certainty and with great accuracy.
Further objects and advantages are to be able to provide adjusting bolts that are commercially available, allowing for easy replacement should they be lost or damaged.
REFERENCES:
patent: 825319 (1906-07-01), Hewitt
patent: 1146412 (1915-07-01), Early
patent: 2192750 (1940-03-01), Mead
patent: 2754593 (1956-07-01), Sundblad
patent: 3110108 (1963-11-01), Sundblad
patent: 4103429 (1978-08-01), Wagoner
patent: 4835875 (1989-06-01), Fuller
patent: 4924592 (1990-05-01), Fuller
patent: 4945644 (1990-08-01), Fuller
patent: 5197199 (1993-03-01), Shrader
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