Plate sundial with installation indicia

A typical plate and gnomon sundial with an enlarged dial plate and an extended gnomon is provided with latitude and longitude displacement indicia lines on the dial plate, beneath the gnomon and beyond the time indicia. A point is established on the gnomon from which a plumb line to the latitude and longitude displacement indicia lines can be determined. The latitude and longitude displacement indicia lines are placed so that when a plumb line from the point on the gnomon intersects the point of intersection of the site latitude indicium line with the site longitude displacement indicium line, the gnomon will be inclined to the horizontal at an angle equal to the latitude of the site and the plane(s) containing the gnomon and the 12 o'clock noon indicium line(s) will be inclined to a vertical plane containing the gnomon at an angle equal to the difference between the longitude of the site and the longitude of the time zone meridian. Set up is accomplished at the site by plumbing from the point on the gnomon to the point of intersection of the site latitude and site longitude displacement indicia lines, and while holding this attitude rotating the sundial on a horizontal surface until the correct zone time is indicated by the shadow of the gnomon from the sun on the time indicia. This will mean that the sundial is correctly oriented and will continue to indicate correct zone time.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is a plate type sundial which indicates time of day 
by the shadow of a gnomon from the sun on a dial plate with an improvement 
to facilitate installation for indication of time in a broad range of 
latitudes and longitudes. 
2. Description of the Prior Art 
Sundials indicating local apparent time have been used for thousands of 
years in myriad shapes, styles, and designs. When standard time zones were 
adopted about a hundred years ago sundials were no longer of major 
importance as timekeepers. Their principal use now is ornamental. To 
indicate zone time at a particular site the plate sundial must be custom 
manufactured for that site, or it must be expertly installed to adjust the 
attitude for the difference between the design latitude and the site 
latitude and for the difference between the longitude of the time zone 
meridian and the longitude of the site meridian. 
This inventor has received a Notice of allowance for a patent of a 
cylindrical sundial with installation indicia, and has filed an 
application for a patent of a hemispherical sundial with installation 
indicia. 
SUMMARY OF THE INVENTION 
The object of the invention is to provide an ornamental, universal, and 
economical plate type sundial which can easily be set up by the average 
person to indicate time-zone time at the site of the instrument. 
The present invention provides latitude and longitudinal indicia so the 
attitude of the sundial can be set for the site by use of a plumb line. 
Once the attitude is set the sundial can be oriented by rotating on a 
horizontal surface until the correct zone time is indicated by the shadow 
of the gnomon from the sun. When secured in the correct attitude and 
orientation, the sundial will continue to indicate correct zone time.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention consists essentially of a dial plate 1 and a gnomon 
2. Reference character 3 is an index point on the longitudinal centerline 
of dial plate 1. 
Gnomon 2 is perpendicular to dial plate 1 and thus an upper edge 4 inclined 
to dial plate 1 at an angle .DELTA.. The longitudinal centerline of upper 
edge 4 intersects dial plate 1 at index point 3. The value of .DELTA. is 
not critical but ideally should equal the latitude of the site. For 
extreme northern and southern sites in the contiguous United States. a 
.DELTA. equal to 35.degree. causes no loss of time indication for six 
months and only up to about one hour of loss at the beginning and end of 
day at one of the solstices. Reference character 5 is a reference point on 
the longitudinal centerline of upper edge 4 of gnomon 2. 
When the longitudinal centerline of upper edge 4 is parallel to the axis of 
the earth, it will be inclined to the horizontal at an angle equal to the 
latitude of the site. Latitude indicia lines 6 are circular arcs on dial 
plate 1 located from index point 3 a distance of: L.times.sin 
(90.degree.-latitude)/sin (90.degree.+latitude-.DELTA.), where L is the 
distance between index point 3 and reference point 5. 
When the longitudinal centerline of upper edge 4 is parallel to the axis of 
the earth and a plumb line from reference point 5 intersects the 
longitudinal centerline of dial plate 1, then the longitudinal centerline 
of dial plate 1 and the longitudinal centerline of upper edge 4 will be in 
the same plane as the merdian of the site. By revolving the entire sundial 
about the longitudinal centerline of upper edge 4 at an angle equal to the 
difference between the longitude of the site and the longitude of the time 
zone meridian, the plane containing the longitudinal centerline of upper 
edge 4 and the longitudinal centerline of dial plate 1 will be made 
parallel to the plane through the time zone meridian. Longitude 
displacement indicia lines 7 are located on dial plate 1 radially from 
index point 3 at an angle from the longitudinal centerline of dial plate 1 
of: tan.sup.31 1 (sin .DELTA.x.times.tan longitude displacement), where 
longitude displacement is the difference between the longitude of the site 
meridian and the longitude of the time zone meridian. 
Time indicia lines 8 are located on dial plate 1 by conventional means 
using the longitudinal centerline of dial plate 1, index point 3, and 
upper edge 4 of the gnomon as bases. 
Reference character 9 is a removable and adjustable plumb line from 
reference point 5 to dial plate 1. 
To set up the sundial, reference point 5 is plumbed directly over the point 
of intersection of site latitude indicium line 6 with site longitude 
displacement indicium line 7. Then while maintaining this attitude the 
sundial is rotated until the correct zone time is indicated by the shadow 
of the gnomon from the sun. The longitudinal centerline of upper edge 4 
will then be parallel to the axis of the earth, and the plane containing 
the longitudinal centerline of upper edge 4 and the longitudinal 
centerline of dial plate 1 will be parallel to the plane of the time zone 
meridian. When secured in this attitude and orientation the sundial will 
continue to indicate the correct zone time. 
In the preferred embodiment adjusting bolts 10 are used to adjust the 
attitude of the sundial on the horizontal top surface of stationary 
support 11, and the sundial is secured by use of a castable material about 
dial plate 1.