IMPROVEMENTS IN TERRESTRIAL GLOBES
Year: 1879

page_text: PROVISIONAL SPECIFICATION left by George Frederick Redfern at the
Office of the Commissioners of Patents on the 7th May 1879. A communi-
cation from abroad by Mungo Turnbull and James Foster, of Toronto, in the
Province of Ontario and Dominion of Canada.
GEORGE FREDERICK REDFERN, of the General Patent Office, 4, South Street,
Finsbury, in the County of Middlesex, Patent Agent. "IMPROVEMENTS IN
TERRESTRIAL GLOBES." [A communication from abroad by Mungo Turnbull and
James Foster, of Toronto, in the Province of Ontario and Dominion of Canada.]
This Invention has relation to improvements in educational terrestrial globes,
and consists, first, in providing the said globe with a zone or ring representing the
terrestrial twilight; secondly, in providing the said globe with a revolving ecliptic,
which exhibits the position of the sun; thirdly, with a moveable solar meridian,
which shows for every day the angular change that takes place between the
ecliptical polar axis and that of the earth's; fourthly, with mechanism for producing
the motion of the solar meridian over the position of the sun, giving his declinations
north or south; fifthly, providing the globe with an azimuth circle, placed between
the ecliptic and the earth, for showing at any point on the earth the sun's altitude
at any hour on each side of the meridian where he is visible; sixthly, in providing
said globe with an axial vernier, having a graduated circle around the south pole
for reading terrestrial longitude in either hours of time or in degrees of an arc, all
of which will be hereinafter fully described.
The objects sought to be accomplished by this improved manner of mounting the
globe are to extend its usefulness as an assistant in the study of geography, and one
of the leading features aimed at is to bring before the eye of the student, by
mechanical appliances, & representation of the causes from whence all these changes
which the different parts of the earth's surface undergo relative to light and heat
during the year, and also to enable the student to solve some new and useful
geographical problems not solvable by any other educational globe heretofore con-
structed. To accomplish these results the axial inclination of the earth to the
ecliptic is adopted, and that plane or pathway of the sun in the heavens is substi-
tuted for the old plan of using the wooden horizon.
The great circle, consisting of an outer circle and an inner circle, represents the
ecliptic plane. The outer circle is fixed to the tripod, and upon it is marked the
twelve constellations of the zodiac, divided into thirty degrees each, and also

page_text: the annual calendar of days. Every degree is opposite to the day of the month
where the sun's centre is situated at the time. The inner brass circle revolves
around the globe upon friction-rollers connected to the under side of the outer circle,
and carries the sun's centre and all the other mechanical appendages. A dark zone
or ring surrounds the globe, and is eighteen degrees broad, and represents the
terrestrial twilight, and is fixed to the revolving ecliptic at right angles thereto.
The edge of this zone next to the position of the sun is always over the centre of
the globe, and exactly ninety degrees away from the sun's centre. Hence as the
sun illuminates but one hemisphere of the earth at any instant, the edge or beginning
of twilight gives accurately the boundary of sunlight and the beginning of darkness
around the earth for every day in the year. The opposite edge of the zone at the
same time shows when the beginning and end of twilight takes place upon any
parallel of latitude in the hemisphere of midnight darkness. A brass semicircle is
graduated and permanently fixed from pole to pole of. the globe. This semicircle
always represents the true position of the solar meridian as it is carried around the
stationary ecliptic by the sun's centre between two friction-pins placed on each
side of the said centre, and, being a moveable meridian with the sun, it serves to
show for every day the angular changes which take place between the ecliptical
polar axis and the earth's axis. The graduated solar meridian has also another
distinct important notion as it revolves with the sun. In its motion the degrees
rise and sink alternately upon the fixed ecliptic plane, and thus reads off the solar
declinations from the equator, and illustrates the astronomical doctrine that the sun
apparently shifts in declination toward the north while it is moving through the
ascending signs of the ecliptic from Capricorn to Cancer, and descends daily south
while passing through the descending signs from Cancer to Capricorn.
A device for indicating the position of the sun is attached to the revolving inner
ecliptical circle, and consists of a brass ring having a fine wire traversing it
diametrically, which reads off the ecliptical place of the sun's centre for the day of
the month required in the calendar. The divided semi-circle revolves with the sun
in the ecliptic, and at the same time has a motion around his centre, and is graduated
into two quadrants of ninety degrees each. In practical geography these quadrants
will give approximately the distance in degrees of any place from sunrise or sunset,
on any parallel of latitude where the sun is visible.
A circle is placed upon the south polar axis of the globe, and is divided into three
hundred and sixty degrees of longitude, and also into hours of civil time. A bracket
or brass arim carries the circle around with the revolving solar meridian, so that
twelve o'clock noon is always with the sun's centre, which is the true zero for
reading the longitude of any meridian, either east or west, on the globe.
A handle is provided for giving the globe axial motion and for working problems
in practical geography. The terrestrial hour-hand can be shifted and fixed by a
screw to the axis of the globe to suit any meridian. This hand or pointer revolves,
when fixed to any meridian, upon the upper face of the circle, and points off, as
required, the hours in civil time, or the degrees in longitude, either east or west, of
the solar meridian.
The standard is secured upon a base, and this standard, which is adjustable by
means of screws, supports the globe.and its axis at the required astronomical angle
to the ecliptic, namely, twenty three degrees twenty eight minutes of an arc,
thereby giving for every day in the year an eye illustration of the parallelism of the
earth's axis, and all the consequences of the seasons which are annually experienced.
The semicircle represents the plane in which the axis of the ecliptic is situated.
This axis is ninety degrees from the sun's centre, and around it the twilight-zone
or daylight-terminator revolves with the sun. The pole of the ecliptic forms the
principal standard of reference to trace the constant changing angles which the
earth's axis makes with it in completing a revolution around the sun. The north
pole of the earth revolves around this axis in twenty five thousand nine hundred
and seventy two years. This motion is known in astronomy as the "precession of
the equinoxes," that is, the vernal equinox or first of Aries, shifts westward on the

page_text: ecliptic at the rate of fifty seconds of an arc annually. The above period is the
great solar cycle.
To show briefly what are the scientific uses of this globe in geographical investi-
gations, the scientific properties of the dark broad ring are selected. This ring
represents continually the width and position of that band or zone of faint refracted
light known as the "terrestrial twilight." It extends in width to an arc on the
earth's surface of eighteen degrees, or one thousand two hundred and fifty English
miles, geometrically, to all places on the globe below the edge of this zone next the
sun's place in the ecliptic. That luminary is either rising or setting as the different
places happen to be in either the eastern or western hemisphere at the time. Hence
it forms the chief geographical nonious to point out for every instant the true.
astronomical time of the dawn of the twilight, also the sunrise and sunset, and the
end of twilight or the beginning of midnight darkness to any place directly below
its edge.
In the old plan of mounting without this appendage these problems cannot be
solved.
Again, problem. Any place being given on the globe to find at what time the
twilight dawned and the sun rose, and when it set and the twilight ended at that
place.
Example. With the revolving ecliptic set the device, which represents the
position of the sun, opposite to the chosen day in the annual calendar, then bring.
the place on the globe to the given apparent or solar meridian for the day, which
done, screw the vernier fast to the earth's axis when it points to the same meridian;
then by bringing back the place on the earth to the two edges of the eastern
morning twilight zone the correct astronomical time of the dawn of twilight and
sunrise will be read off' by the vernier in hours and degrees on the graduated circle
around the south polar axis of the earth, and by turning the globe west till the
assumed place reaches the opposite part of the zone, the exact time of the evening
vicissitudes of sunset and the end of twilight will also be correctly given.
Moreover, in the study of terrestrial geography, it has other uses than that of
being an exact resolver of longitude, or for giving civil time to any place.
To the sight it acts the part of a great distributor of light and heat on the ter-
restrial illuminated surface, which is shown to be reciprocal over the two hemispheres ;
for as the sun apparently moves from the winter to the summer solstice, from
Capricorn to Cancer, it brings into view how the versed sines of the different
parallels of latitude come into the sun's light over all the northern portion of the
globe, while in the southern, during the time, the phenomena is reversed.
In fact,
with this scientific appendage the pupil can always place himself directly between
the sun and the earth, and all its different phases, for every day in the year, pass
before him like a well directed panorama; hence the motion of the material repre-
sentation of the twilight sky around the globe forms one of the principal improve-
ments claimed for this educational instrument.
Another new arrangement is the substitution of the plane of the ecliptic for the
old wooden horizon around the globe.
In the Copernican description or system of the universe it is well known that
the ecliptic plane forms the chief and surest place of reference to trace the mechanical
position of all physical things around us, whether they are to be found on the surface
of the earth, or to be seen in the heavens. Consequently, the apparent motion of
the sun in this plane being invariable, and at the same time around the exact
inclined terrestrial axis, as shown, and regulating all the other mechanical appen-
dages, gives a perfect transparency and simplicity to the solution of problems
hitherto complicated, not only in geography but in its sister branch of learning,
elementary astronomy.
To the inhabitants of the northern hemisphere it can be well shewn that the
sunlight history of the north pole of our globe forms the grand centre around
which the cause of the seasons revolve. By its motion within and without the

page_text: twilight region, especially at the four principal annual epochs of time, the illustra-
tion becomes very complete. For example, at the winter solstice (December 22),
how the pole is seen to be thrown over twenty three and a half degrees into the
dark hemisphere, where within the entire arctic surface it is hid from view; then
at the vernal equinox (March 20) the pole is just seen emerging from its five
months' darkness, thus causing equal days and nights over all the earth. Again,
at the summer solstice (June 21), the pole having reached the position of being
twenty-three and a half degrees from the twilight zone, the whole of the frigid
zone becomes illuminated by a sun which for a time cannot set, and during the
period we have in the north the pleasant months of summer. In the next six
months' motion the preceding order of things will be completely reversed till the
sun arrives again at the winter solstice to commence anew his annual course.
It is worthy of notice that during the year the twilight sky sweeps twice over
the two frigid zones of the globe, but over the other three it moves only once in the
same time.
In reference to the three other mechanical arrangements formerly mentioned,
relative to the solution of the solar declinations and finding the sun's azimuth at
any time and place, along with the process to trace the longitude on the globe in
hours or in degrees of an arc, the mere inspection of the different appendages will
suffice to show the humblest student the way to make them serviceable for what
they are respectively intended to solve.