Improved Sun Dial.
Year: 1892

page_text: Date of Application, 13th May, 1892-Accepted, 18th June, 1892
Improved Sun Dial.
I, CHARLES EDOUARD CHAMBERLAND, of 145 Rue de Rennes, Paris, Manager
at the Pasteur Institute, do hereby declare the nature of this invention and in what
manner the saine is to be performed to be particularly described and ascertained in
and by the following statement :-
This invention has for object to provide a cheap portable sun dial capable of
being located at any part of the globe and of being adjusted by means of the
indications of the apparatus itself, without it being necessary to have recourse
either to the indications of the compass, or to know the solar time. My improved
apparatus thus constitutes a real solar clock.
The improved sun dial is illustrated, by way of example only, in the accompanying
drawings in which,
Fig. 1 is a perspective view of the apparatus from the side of the front face of
the dial;
Fig. 2 shows in perspective the same apparatus seen from the side of the rear
face of the dial;
Fig. 3 is a table or scale preferably inscribed upon the front face of the dial and
giving the corrections in minutes which are to be made in the actual solar time
indicated by the apparatus in order to know the mean time corresponding to the
indications of ordinary clocks;
Fig. 4 is another table or scale to be preferably inscribed on the rear face of the
dial, giving the necessary indications for adjusting the apparatus ;
Fig.
5 is a diagram to which reference will be made hereinafter in explaining the
principle of the apparatus.
The use of the two tables will be clearly described hereinafter.
The apparatus consists of the dial proper a which may be constructed of any
suitable material such as metal, glass, wood, pasteboard, etc. and which rests with
its straight edge x-y on a horizontal plane. The dial a is traversed by a flat
stem b which is perpendicular to the plane of the dial and one of the edges
of which passes through the centre of the said dial. Upon the stem b there
slides an arc-shaped link c in which is formed an arc-shaped slot d; into this slot
enter the spindles of two screws e, e, which are screwed into the stem 6 near the
ends of the latter, and the heads of which allow of fixing the movable arc in any
desired position with relation to the dial a and to the stem b.
с
The stem b may be fixed to the dial a either (as shown in the drawing), by means
of two set screws which pass through the dial a and engage in a shoulder g formed
in one with the stem b, or in any other suitable manner.
C
The link (whose object is to allow of imparting more or less inclination to the
apparatus according to the latitude of the place where the apparatus is located)
It is obvious that this
is illustrated in the drawing as passing through the dial a.
link need not pass through the dial. It could for instance constitute a simple
extension of the rear part of the stem b upon which it might be rigidly fixed
(in such a manner as to impart to the apparatus an inclination determined once
for all to correspond to a given latitude) or upon which it might be mounted in
link fashion as shown in the drawing, so as to allow of using the instrument in all
latitudes.
The dial a, the stem 6 and the link c are provided with scale divisions the object
of which will be explained hereinafter.
Assuming that at a given place on the earth the apparatus be arranged in such a
thuouch the centre of the dial (which edge I shall

page_text: term "hour axis") be placed in the direction of the axis of the earth. The plane
of the dial will then represent the plane of the equator. The sun will turn
around the axis in twenty-four hours so that the shadow projected by the hour axis
on the dial will move in one hour through a distance of 260 or 15 degrees.
The subdivisions of the arc of 15 degrees will give the subdivisions of the
hour. The dial a will then bear a regular graduation of 24 hours and
subdivisions.
The principal question is to adjust the dial in such a manner that the "hour
axis" shall be in the same direction as the axis of the earth.
Assuming this adjustment to have been made then if the "hour axis" is
prolonged until it meets the horizontal plane A (Fig. 5); the angle A is the angle
of latitude, and as in the triangle A O B, the angle O is a right angle, the angle B
is consequently the complimentary angle of the latitude. Now according to the
construction of the apparatus, the centre of the movable arc c is at B, then the
portion of the arc c comprised between the horizontal plane and the dial a is a
known arc, because the latitude of the place is given either by the Annual of the
Office of Longitudes, or by geographical maps, and it will be sufficient to take the
compliment thereof in order to obtain the length of the arc which should be com-
prised between the horizontal plane and the dial a. It will be then easy, by sliding
the arc c upon the stem b, to determine (with the aid of the graduation in degrees
inscribed thereon) the position of said arc with relation to the dial and to fix it in
position by tightening the screws e, e.
The apparatus being thus regulated for the latitude of the place where the
observer is situated, the hour axis must then be directed along the line north-south
in order to bring it into the direction of the axis of the earth. Assuming always
that the apparatus be adjusted at a certain spot on the globe and let S (see Fig. 5)
be the position of the sun for a specified day. The rays of the sun in just touching
the borders C of the dial, will project upon the "hour axis" a certain shadow OD,
and the angle OCD will be the angle of declination of the sun for said day. If
the length OC is fixed, that is to say, if the dial is in the form of a circle, as in
Figs. 1 and 2, the result will be that the length O D will remain practically fixed
during the whole of the day because the declination of the sun does not vary
appreciably in the course of the day. Then if the length O D for a given day
were known, it would be sufficient, in order to adjust the sun dial (previously
adjusted to the latitude of the place) on said day, to turn it on the horizontal plane
(about the point B) until the shadow projected by the border C of the dial upon
the hour axis coincides with the length O D assumed to be known. Now, in the
right-angle triangle OCD, O D=0C tg C. OC is known, also the angle C is
known, because the angle of declination of the sun is given every day in the year by
the Annual of the Office of Longitudes. It is therefore easy to make a table giving
the lengths O D for the several days of the year.
Moreover it should be remarked that the angles of declination of the sun for the
various days of the year do not vary appreciably from one year to the other. In
fact calculation shows that if a table of the averages or means of the angles of
declination for a great number of years be made, the greatest difference between
the mean angles thus obtained and the true angles is about 10 minutes, which
corresponds to the variation of about millimetre in the length of O. D. assuming
the radius OC of the dial to be equal to 10%m-
This difference may therefore be neglected in practice and it is easy to make a
perpetual table giving the lengths O D for every day in the year.
The table shown in Fig. 4 (and which is preferably printed on the rear face of the
dial) indicates in millimetres the lengths OD for the 1st, 6th, 11, 16, 21, and 26th
of each month. By interpolation it will be easy to obtain the length corresponding
to an intermediate day. With the object of effecting ready adjustment of the dial,
the stem 6 carries inscribed upon the line "hour axis" a scale in millimetres, the 5
divisions of which start from O from the front face of the dial in one direction, and
from the rear face of the same dial in the other direction. It will therefore be

page_text: easy, when the apparatus has been regulated as to latitude, to make it rotate on its
base about a vertical axis, until the shadow O D produced by the border C of the
dial from the hour axis reaches, on the scale, the length indicated by the table,
(Fig. 4) for the respective day. The apparatus will then be normally adjusted
and it will only be necessary to read the indications thereof.
For this purpose, it
may be stated that the sun in turning around the hour axis, does not remain
constantly on the same side of the plane of the dial. On March 21 the day of the
spring equinox, the sun moves exactly in the plane of the dial; then on the following
days it rises forward of the plane of the dial in such a manner that the angles of
declination increase, and in consequence the lengths O D increase. This is so
until June 21st the time of the summer solstice, when the angle of declination is at
the maximum (about 23° 23'); then the sun moves down again, passes anew through
the same phases as before, and is again in the plane of the dial on the
21st September, the day of the autumn equinox.
It thus continues to descend, and passes to the rear of the plane of the dial.
From that moment, the lengths O D are projected upon the hour axis forward of
the dial, and the whole front face of the dial is in shadow. The sun continues to
descend so as to reach on the 21 December the day of the winter solstice, a maximum
declination equal to, but in a contrary direction to the declination of the summer
solstice. Then the sun commences to reascend and returns into the plane of the
dial on the 21st March to recommence the same course as before.
.
After the preceding explanations, it will be understood that during 6 months in
the year, (from 21st September to 21st March) the sun turns to the rear of the
plane of the dial so that during that time, the shadow cast by the hour axis is
projected upon the rear face of the dial. In order to avoid having to inscribe a
scale upon said rear face, and especially in order to be able to read off the shadow
conveniently, the apparatus may be constructed of a translucent material such as
dull glass etc. I however prefer to employ the mode of construction illustrated in
the accompanying drawing, recessing or cutting out the lower part of the dial (as
shown at h in Figs. 1 and 2) along the inner border of the scale. The lower edge
of the recess h thus formed is folded back in such a manner as to form a border i
upon which is projected a part of the shadow cast by the hour axis upon the rear
face of the dial; the shadow thus comes into direct contact with the divisions of
the forward face and can be very easily read off from said latter face. It will be
noted that it is sufficient to recess the dial along the line 6 o'clock in the orning-
6 o'clock in the evening because in the winter the days are of less than 12 hours
duration.
Finally regard should be had as to whether the time indicated by the dial is the
exact solar time or true time. This hour is not that which ought to be indicated
by clocks, because the duration of the solar day is not the same at different times
of the year. Clocks therefore could not be set to the solar time; they would have
to be sometimes put forward and sometimes put back. It is for this reason that
ordinary clocks indicate the mean time, that is to say, the time of a fictitious sun
which, starting from the same point of the ecliptic as the true sun, would return to
the same point at the end of a year. As the differences between true solar time
and mean time do not vary appreciably from one year to the other, I have made a
second table (shown in Fig. 3). This table (which is preferably printed on the
front face of the dial) gives for the 1st, 6th, 11th, 16th, 21st and 26th of each
month the number of minutes which should be added to or subtracted from the solar
time indicated by the dial in order to have the mean time.
By interpolation it will be easy to obtain the intermediate numbers corresponding
to each day in the year.
The numbers which are preceded by the sign (+) in the table (Fig. 3) should be
added to the solar time read off the dial.
The numbers which have the sign (-) prefixed should be subtracted from the
time indicated by the dial.

page_text: Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
A sun dial capable of being adjusted without it being necessary for this purpose
to know the solar time or to employ a compass, and comprising a circular dial (a)
recessed, and provided, if required, at the lower edge of said recess (h), with a
projecting border (i); an hour axis (b) fixed perpendicularly to the plane of the
dial, one of the edges of which passes through the centre of the said dial and upon
which is mounted an arc shaped link (c) the rear end of which rests on a horizontal
plane, said link having a graduated scale for facilitating the regulation of the
inclination of the apparatus according to the various latitudes, and said hour axis b
having at each side of the dial, a straight scale for facilitating the adjustment of
the apparatus by turning it in such a manner that the length of the shadow cast by
the dial, on either side, on the hour axis, shall agree with the length calculated
beforehand and indicated for each time of the year by a table upon the apparatus,
and said dial being provided with a table of corrections, giving for each time of the
year, the number of minutes which must be added to or subtracted from the real
solar time indicated by the dial in order to obtain the mean time of clocks
substantially as described.
Dated this 13th day of May 1892
C. E. CHAMBERLAND,
By L. W., per F. B.

page_text: |JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
14,25 3,05 1,30 0,80 2,70 4,05 4,25 3,25 1,45 0,602,604,00
64,15 2,75 1,00 1,15 2,95 4,15 4,15 3,00 1,15 0,90 2,90 4,15|
114,00 2,500,65 1,45 3,25 4.25 4,05 2,70 0,80 1,25 3,15 4,25
163,802,15 0.30 1.80 3,454,30 3,902,45 0,45 1,55 3,40 4,30
213,60 1,85 0,05 2.15 3.70 4,35 8,75 2,15 0,10 1,90 3,65 4,35
263.40 1,500.402.4
2.40 3.85 4,35 3,55 1,85 0.25 2.25 3,85 4.35
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