IMPROVED APPARATUS FOR ASCERTAINING THE TIME OF DAY BY THE POSITION OF THE SUN
Year: 1878

page_text: PROVISIONAL SPECIFICATION left by Halliday Macartney at the Office
of the Commissioners of Patents on the 4th January 1878.
HALLIDAY MACARTNEY, of Portland Place, in the County of Middlesex, Doctor of
Medicine. "IMPROVED APPARATUS FOR ASCERTAINING THE TIME OF DAY BY THE
POSITION OF THE SUN."
The object of this Invention is to provide a ready means for ascertaining the
longitude of any spot, whether on land or sea, by one observation, and at any time
when the sun's rays are visible. To this end I provide an instrument which may
be described as a compass box, the lid of which is fitted with a clock dial, and hour,
minute, and seconds hand, which are capable of being worked by suitable spur
gearing, the latter being operated by turning a milled headed spindle.
Standing up from the centre of the clock face through the tubes which carry the
hands is a style, also moved by the casing, and provided with a cross pin to receive
the notched standard of a tube that is hinged thereto. This tube is closed at both
ends, but is open for a short distance at the upper side, and near one end thereof,
to bring the interior into view. The opposite end of the tube has a fine vertical slit
made in it.
A diaphragm is inserted in the tube near the top opening, and in it is made a
corresponding slit for the purpose to be presently explained.
The dial with its mechanism is hinged to the compass box, and a graduated sector
(hinged to the box) is provided to facilitate the adjustment at any desired angle to
the plane of the dial, and consequently of the style which carries the tube. This
compass box is fitted with adjustable supports, and with spirit levels to ensure the
accurate setting of the instrument horizontally when an observation is to be taken,
and the compass card and dial are so arranged relatively to each other that the
north and south poles of the card will correspond with the hours VI. and XII. of
the dial.
Supposing that it is desired to take an observation (the sun being favourable) to
ascertain the time of day at a spot the latitude of which is known, I set the dial face
to the latitude as indicated on the sector, and bring the compass to bear due north
and south. I then adjust the tube so as to bring its slit end opposite the sun, and

page_text: having intercepted a ray of light, which after traversing the corresponding slit in
the diaphragm strikes against the opposite and closed end of the tube, I turn the
style by means of the milled headed spindle until the width of the ray after
gradually diminishing comes to the vanishing point. I now refer to the hands,
which having followed the movements of the style carrying the tube will be found
standing at the hour, minute, and second of solar time, and thus I find the time of
day indicated by the sun. By comparing this time with a chronometer denoting
Greenwich time, and making allowance for the equation of time, I readily ascertain
the longitude of the place east or west of Greenwich at which the observation was
taken.
It should be remarked that if the dial is as I have supposed divided like that of
an ordinary clock into twelve hours, the style must be speeded to move at half the
rate of the hour hand.
When operating on shipboard the instrument must be supported on a table carried
by gimbals, and this table may be conveniently weighted by a central pendulum to
increase its stability.