An Improved Universal Diurnal and Geographical Clock, more especially applicable as a Map or for Educational Purposes.
Year: 1896

page_text: Date of Application, 31st Mar., 1896-Accepted, 6th June, 1896
COMPLETE SPECIFICATION.
An Improved Universal Diurnal and Geographical Clock, more
especially applicable as a Map or for Educational Purposes.
I, DAVID WALLACE THOMPSON, of 326 Sixty-first Place, Chicago, in the
County of Cook, State of Illinois, United States of America, Manufacturer, do
hereby declare the nature of this invention and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:-
The object of my invention is to provide for the use of educational institutions a
clock that will indicate to the eye, in addition to the local time of the place, the
time of day or night in all parts of the world; the portion of the earth's surface
where daylight prevails and the portion where night prevails; and capable of
adjustment to illustrate the same for all seasons of the year and all latitudes, and
which shall also illustrate to the eye the rising and setting of the sun in all latitudes
and seasons of the year showing where, when, and why six months day and six
months night prevails near the poles; the summer and winter solstices; the
autumnal and vernal equinoxes and, in fact, all terrestrial phenomena dependent
upon the inclination of the earth's axis to the ecliptic, and the revolution of the
earth.
To these ends my invention consists of an artificial shadow or screen, the form
of which can be changed or adjusted to correspond to the shape of the shadow at all
seasons of the year, in combination with a map of the circumpolar hemisphere divided
into hours of longitude, and connected to rotate with the hour hand of a twenty-four
hour clock whose dial is numbered in two consecutive series of figures from 1 to 12,
to represent the twelve hours of day and twelve hours of night, all as hereinafter
more fully described.
Figure 1 is a face of a clock constructed in accordance with my invention,
equipped for the northern hemisphere and arranged for rotation reversely to the
ordinary motion of a clock.
Figure 2 is a similar view of a clock face equipped for the southern hemisphere
with the hands arranged to rotate in the opposite direction or usual way.
Figure 3 is a section through the line x-x of Figure 1.
Figure 4 shows a series of the shadow plates marked to indicate the month
united as a continuous strip or ribbon, and Figure 5 shows how these may be
arranged in the clock upon rolls.
Referring to Figure 1, A represents the dial of a twenty-four hour clock, which
is numbered in two series of figures from 1 to 12 following each other and
progressing in direction reverse to that of the ordinary clock. B is the hour, and
C the minute hand of the clock, which are geared in the usual way, except that
the hour hand revolves but once (and not twice, as usual) in the twenty-four hours.
To the hour haud is attached concentrically, to move with it, a disk D upon which
is delineated the circumpolar hemisphere representing in Figure 1, the northern
half of the earth's surface. This map is divided by radial lines from the pole into
divisions of longitude representing fifteen degrees (15°) each, which are numbered
progressively both ways for east and west longitude from zero (0) on one side of
the earth to one hundred and eighty degrees (180°) on the opposite side the
numbers increasing by fifteen degrees (15°). The spaces between these divisions
of longitude are fifteen degrees (15°), each of which represents in the
revolution of the earth, just one hour of time, so that these spaces or longitude

page_text: lines are correlated to. the twenty-four hour subdivisions of the dial to couple the
subdivisions of time with the various localities on the map.
E is a plate of semi-transparent material such as colored mica, horn, celluloid, or
other similar substance which can be made to represent the shadow or shaded
portion of the earth's surface to indicate night, and still be sufficiently transparent
to allow the localities on the map to be read through the same. This artificial
or representative shadow is fixed to the face of the clock so as to be stationary, and
yet is made detached so as to permit other shapes of shadow to be substituted,
for it will be understood that such shadow will only appear semi-circular with a
straight diameter at the two periods of the year, representing the vernal and
autumnal equinoxes. At other times it will be greater or less than a semi-circle
dependent upon the angles of the ecliptic and which end of the earth is turned
toward the observer.
Referring to Figure 1, it will be perceived that the side of the earth containing
the western hemisphere is turned toward the sun and over that arca it is day, while
upon the opposite side covered by the screen or shadow it is night. The juncture
of the line of light and darkness is, as shown, a straight, diametrical line, and with
the earth turning in the direction of the arrow the line represents on the left
"morning," where the earth is turning into the light; while upon the right where
the earth is turning out of the light and into the shadow, it is "evening" or
twilight. Midway between these points on the light side it is "noon," and at a
diametrical point on the shadow it is "midnight."
Now to know what time of day or night it is at any point on the earth's surface,
it is only necessary to extend radially the longitude. line of the place to the outer
figures of the clock dial, whether it be in the shadow or light, the apportionment
of the longitude of the earth in hour subdivisions (15°) to correspond with the
twenty-four numbers, permitting this to be instantly observed without calculation.
To enable the eye to follow the radial position of the clock dial figures, inward
across the surface of the earth, the glass face g of the clock should have radial lines
engraved or etched thereon, and converging from the several twenty-four marks
inwardly to the pole.
When the day and night are equal, the line separating the light and dark side
of the earth will be a straight diametrical line passing through the poles as in
Figure 1, which occurs at the periods of vernal and autumnal equinox. At other
times one pole will be a region of continual day, and the other one of continual
night, for a period of six months. This is due to the angles of the earth's axis, or
the ecliptic, which holds one pole toward the sun through the complete
revolution of the earth, and the other in the shadow for the same length of time.
To illustrate this I now refer to Figure 2, which shows the southern hemisphere in-
which the map revolves in the usual direction of the clock hands, and in which the
shadow is shown in the position of the summer and winter solstice. As shown,
the south pole is wholly within the light, and there is no night. for six months.
The dotted curved line shows the position of the shadow after six months have
elapsed, and the movement of the earth in its orbit has reversed the angle of the
ecliptic, thus representing the south pole continually in the shadow for six
months.
In the use of my invention I prefer to append the ordinary hour and minute
hand, but it is obvious that these are not essential features of my invention, since
the geographical location by radiating lines of longitude constitute so many
pointers to the several twenty-four hours of the clock dial, as to be sufficient, and
the hour and minute hand are only put on to enable the observer to note his local
time by easy effort at a more or less remote point from the clock. The shadow
plates are constructed as a continuous strip or ribbon, as in Figure 4, which is
arranged upon rolls as in Figure 5, to be fed successively across the face of the
dial to illustrate the different phases of the shadow.
The dial may be used without an actuating time piece and without hands, as an
educational chart, and in such case it will be contained in a frame as indicated in

page_text: dotted lines in Figure 1 and a notch n will allow access to the periphery of the
map to rotate it, or any other means for rotating it may be used.
By applying the single shadow plate to one-half of the circumpolar map, a
single plate is made to indicate a complete cycle of day and night in a very simple,
practical, correct and graphic way, and I am enabled also to indicate the different
phases of the night shadows along its edge.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :
The combination with a circumpolar map made revoluble about a central axis,
of a series of movable material representations of the shadowed portion of the earth's
surface applied to one-half of said map, and made in the form of a continuous strip
having along its edge different shapes corresponding to and indicating the different
phases of the earth's shadow, and means for sustaining the same, substantially as
shown and described.
Dated this Seventh day of March 1896.
DAVID WALLACE THOMPSON.
Haseltine, Lake & Co.,
45 Southampton Buildings, London, W.C., Agents for the Applicant.