An Improved Instrument for Surveying with the Aid of Photography.
Year: 1894

page_text: Date of Application, 27th July, 1894
Complete Specification Left, 13th Dec., 1894-Accepted, 6th Apr., 1895
PROVISIONAL SPECIFICATION.
An Improved Instrument for Surveying with the Aid of
Photography.
JOHN BRIDGES LEE M.A. F.G.S. Barrister-at-Law of the Inner Temple
address, Constitutional Club Northumberland Avenue London, do hereby declare
the nature of this invention to be as follows:-
My improved instrument is compounded of (1) A photographic camera and
photographic lens. (2) A graduated compass fitted in the base of the camera and
arranged so as to record photographically the magnetic bearings of objects in the
median vertical plane of the photographic image. (3) A telescope mounted above
the camera capable of rotation in a vertical plane only. The telescope fitted with
cross wires in the eyepiece and carrying an arm or bar the distal end of which
travels over a segment of a graduated circle the readings on which will give the
angular inclination of the telescope in a vertical plane. (4) Cross wires carried
by a light frame which fits inside the camera close in front of sensitive plate or
film when it is in place ready for exposure. The cross wires intersect at right
angles on the optical axis of the photographic lens so that when the camera is
accurately level the vertical wire marks the median vertical plane of the field of
view and the horizontal wire the horizon. (5) Levels outside the camera. The
top and bottom surfaces of the camera must be as nearly as possible parallel
to each other and to the median vertical plane of the whole instrument.
(6) Other necessary fittings adjustments and appliances subsidiary to the general
plan of the instrument and either necessary or useful for perfecting the details of
construction or for facilitating the use and extending the usefulness of the instrument.
My improved instrument in its simplest form is-adaptable for use either alone or
with an ordinary plane table of the simplest construction but with firm steady
supports and good levelling arrangements-or-the instrument constructed as above
indicated in outline may be supported on the vertical axis of a horizontal
graduated circle with subsidiary arrangements for reading horizontal angles such as
are iu common use with theodolites and other allied instruments.
My instrument in its most elaborate and complete form will be in effect a kind of
photographic theodolite and all photographs taken with it will shew the naturab
horizon the median vertical plane of the image the optical centre of the image and
the magnetic bearings of all objects in the median vertical plane of the field
of view.
COMPLETE SPECIFICATION.
An Improved Instrument for Surveying with the Aid of
Photography.
I, JOHN BRIDGES LEE, M.A. Barrister-at-Law of the Inner Temple, present
address, Constitutional Club, Northumberland Avenue, London, 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:
My improved instrument is compounded of (1) A photographic camera and

page_text: photographic lens. (2) A graduated compass fitted in the base of the camera and
arranged so as to record photographically the magnetic bearing of objects in the
median vertical plane of the photographic image. (3) A telescope mounted above
the camera capable. of adjustment in a vertical plane only, the telescope fitted
with cross wires or webs and according to one arrangement carrying an arm or
bar the distal end of which carries a vernier which travels over a segment of a
graduated circle the readings on which will give the angular inclination of the
telescope in a vertical plane. (4) Cross wires hairs or fibres carried by a light
frame which fits inside the camera close in front of sensitive plate or film when it
is in place ready for exposure The cross wires, hairs or fibres intersect at right
angles on the optical axis of the photographic lens so that when the camera is
accurately level the vertical wire marks the median vertical plane of the field of
view and the horizontal wire the horizon. (5) One or more levels outside the
camera. The bottom surface of the camera should be a plane surface and the
camera is best made in the form of a rectangular box. (6) Other necessary fittings
adjustments and appliances subsidiary to the general plan of the instrument and
either necessary or useful for perfecting the details of construction or for facilitating
the use and extending the usefulness of the instrument.
.
My improved instrument in its simplest form is adaptable for use either alone or
with an ordinary plane table of the simplest construction but with. firm steady
supports and good levelling arrangements or the instrument constructed as above
indicated in outline may be supported on the vertical axis of a horizontal graduated
circle with subsidiary arrangements for reading horizontal angles such as are in
common use with theodolites and other allied instruments.
My instrument in its most elaborate and complete form will be in effect a kind of
photographic theodolite and all photographs taken with it will show the horizontal
and the median vertical planes of the instrument marked as straight lines on the
face of the photographic image.
My invention is illustrated in the accompanying drawings in which Figure 1 is a
side view, Figure 2 is a front view, Figure 3 is a vertical longitudinal section,
Figure 4 is a plan and Figure 5 is a back view of a camera fitted with my
improvements, and Figure 6 is a plan of the stand for the same.
In carrying my present invention into effect I prefer to use a box camera a made
of aluminium and provided with a good rectilinear photographic doublet lens and
1 use in combination therewith a compass needle c carrying a vertically divided
cylindrical scale c¹ and I use also a fixed vertical index f all of which are
constructed, arranged, carried and operated in a similar manner to that shown and
described in my Specification No. 11958 of the present year, the letters of
reference on the various parts shown in the accompanying drawings being the same
as those used in the drawings accompanying the above named Specification and
being applicable to the description contained therein. In addition to carrying the
vertical index f the frame falso carries a horizontal wire hair or fibre so that
when the camera is accurately level and the compass structure racked back into the
dark slide e so as to bring the cross wires hairs or fibres f. j against the sensitive
plate or film the vertical wire or index f will photographically mark the median
vertical plane of the field of view and the horizontal wire hair or fibre ; the
horizontal plane which bisects the photographic lens.
I also fix outside on the top of the camera a spirit level which I mount in the
following manner to enable the camera to be adjusted to a horizontal plane by
means of a single tubular spirit level. The level is supported by a metal frame
which has rigidly attached thereto a disc which rests upon a similar disc /* fixed
to the top of the camera in such manner that the surfaces of contact of the two
discs shall be truly parallel to the base of the camera. The two discs h¹ h² are
accurately ground to work in close contact with each other in all positions of the
level; a pin or stud ³ passes down from the disc h' through a hole in the disc h³
and through the top of the camera a and is fitted on the inside of the camera with
a washer having a D or square shaped hole fitting a correspondingly formed part

page_text: of the pin A and a screw is screwed into the bottom end of the pin h* so that by its
head bearing against the washer it shall retain the two discs h¹ h' in working
connection with each other. The two discs h' may however be otherwise retained
in proper relation with each other, and the chief peculiarities and advantages of this
construction and arrangement consist, firstly, in the fact that by employing two
accurately plane surfaces in juxta-position and of sufficient superficial area with
reference to the length of the level, I am able to dispense with the necessity which
might otherwise exist for a deep fitting axis of revolution, and secondly, if the
top surface of the lower disc is made truly parallel to the base of the camera and
the upper disc, which is carried by the level, is accurately adjusted to the lower
fixed dise, it becomes immaterial for the purpose of levelling whether the rest of
the top of the camera has a plaue surface or not.
It is convenient to employ one accurately adjusted tubular level which can
revolve in its own plaue and which is so attached to the instrument that it cannot
accidentally fall off or be easily thrown out of adjustment, rather than two fixed
levels adjusted at right angles to each other, or than loose unattached levels as
often used.
Accurate levelling is of course necessary to secure that the internal cross wires
shall, when in proper adjustment, mark true vertical and horizontal planes on the
photographs, and the construction which I have described I have tried and found
to be efficient and I believe it to be the best construction and arrangement.
The adjusting screws are placed underneath the mounting carrying the spirit tube
and are thereby protected from injury.
A telescope i of any suitable construction is mounted in a frame with capability
of moving in a vertical plane only.
The telescope i is fitted with cross webs fixed in position at right angles to each
other and in vertical and horizontal planes when the instrument has been accurately
levelled and according to the arrangement shown in the drawings has attached
thereto a segment of a graduated circle which travels with the telescope and
moves past a fixed vernier k, the telescope i also carries at the end of an adjustable
arm a magnifying glass through which the divisions on the graduated segment i²
and vernier k can be read with facility. The readings on the segment and vernier
will give the angular inclination of the telescope in a vertical plane. The
periphery of the segment is toothed and a pinion gearing into the same is used
to give motion to the telescope i. The telescope i is shown in the drawings with
an astronomical eye piece but for surveying purposes it will of course be fitted with
a terrestrial or erecting eye piece.
My improved instrument constructed as above described can be used alone or on
an ordinary plane table or stand of the simplest construction but with firm steady
supports and good levelling arrangements or as shown in the drawings the instru-
ment constructed as above described may be supported on a horizontal graduated
circle resting on levelling screws n mounted in the head of a stand m.
In this case the camera a is provided with a downwardly extending screw stud or
axis a passing through a hole in the centre of the circle land through a ball and
socket joint and it can be clamped to the circle by a fly nut a mounted on the
stud or axis a³.
A vernier n is fixed on the lower edge of the back of the camera to enable
minute readings of the scale on the graduated circle / to be made.
By the above arrangements the graduated circle can be first adjusted in position
so that the compass reading and the readings on the horizontal circle correspond
and it can then be fixed and accurately levelled and the camera can be set free to
revolve over the circle and without displacing it from its position so that all
angles read in the horizontal circle will correspond with the bearings recorded on
photographs.
To use my instrument in ordinary cases I adjust it to an approximately level
position on its stand by aid of the tripod legs. I then clamp those legs by the fly

page_text: screws at the head. Next I rotate the camera until the zero of the vernier n
carried by it is at zero on the horizontal circle 1. Then I rack back the compass
structure until the rectangular frame f' which supports the cross fibres fj is in
contact with the focussing screen and wait until the compass scale has come to a
position of rest or nearly so. Then I rotate the horizontal circle 1, carrying the
camera with it, until the vertical fibre f, as seen through the window a' in the
focussing screen, is exactly opposite the zero of the compass scale when at rest.
Then I tighten up the levelling screws m³ so as to clamp the horizontal circle /
firmly in position, and at the same time I take care to secure accurate levelling, the
same screws m² serving to level the horizontal circle and to hold it rigid when
levelled in position. 1 then loosen the fly screw a which works on the vertical
axis a² of the camera, so that the latter can be freely rotated, when, if the preceding
directions have been carried out, the compass readings, as seen through the
window, will in all positions correspond to the readings on the horizontal
circle l.
To determine the exact position of the camera I use a plumb line, which I loop
over the fly screw below the stand head after the instrument has been set up and
adjusted in position.
The instrument can then be used as a theodolite for reading all horizontal angles
and all vertical angles within the vertical range of the telescope i. The horizontal
angles so read will, of course, be the bearings and should (and will if the instrument
has been well made) correspond with the compass readings as observed through the
window x¹.
If now it is desired to take a photographic record of the bearing of any point
and of all objects within the range of the photographic lens right and left and
above and below the selected point, I bring the intersection of the cross webs in
the telescope on the selected point. I then rack forward the compass structure to
get it out of the way, while I substitute a double dark slide charged with sensitive
photographic plates in place of the focussing screen. Then, after taking care that
the photographic lens is properly capped, I open the front shutter of the slide and
rack back the compass structure until the rectangular frame which carries the
vertical and horizontal fibres fj is brought into contact with the sensitive plate.
Again I observe through the telescope to make sure that the intersection of the
webs in the telescope is exactly on the selected point and I wait a minute or two to
give time for the internal compass to come to a perfect state of rest before
uncapping the lens to take a picture. I utilise this minute or two by making notes
of the description of the point-the horizontal angle as read on the horizontal
eircle by the aid of the vernier n, and of the vertical angle as read by the lens **
on the vertical arc i, and at the same time any other notes of interest can be made
concerning the general outlook in the direction toward which the camera is pointed.
After these notes are finished and the compass has had time to come to rest, I take
off and replace the cap in the ordinary way and follow all the well known rules of
photography for exposure, developement, printing, etc., and I obtain a picture which
bears on its face an automatic photographic record of the bearing of any selected
point and of the median vertical plane and of the horizontal plane bisecting the
photographic lens. Preferably I use a very fine stop to ensure sharp definition.
The exact position of any point on the photograph I can determine by simply
measuring with a pair of compasses and scale the correct distance along the vertical
line (above or below the point of intersection as the case may be) which corresponds
with the observed angle of elevation (or depression) noted at the time the photo-
graphic picture was taken. The angular bearings of all other points visible on the
picture can be measured at any time with the aid of a pair of compasses and scale
so that from one photograph a very large number of angular measurements can be
obtained and a single photograph may yield as many angles for surveying purposes
and as much general and accurate information as could be obtained only by a very
large number of measurements and notes and sketching in the field if ordinary

page_text: methods of surveying were employed for mapping the same ground. On pictures
taken with my instrument, one tenth of an inch represents one degree of angle an
the angular bearing of every visible point on the picture from the station point
where the camera was set up, can be determined by adding or subtracting as many
degrees or fractions of a degree to or from the automatically recorded bearing of
the vertical fibre f as there are tenths of an inch between the points on the picture.
and the vertical fibre. Similarly vertical angles can be measured on the same scale..
Strictly speaking the scale for interpreting the picture should be a tangent
scale, but, inasmuch as the maximum angle of any point on the picture is never
more than twenty degrees right or left of the median line, there will be no
appreciable error for ordinary mapping purposes if an ordinary scale divided to
tenths of an inch be used.
It is best of course and most strictly accurate to have an exact scale specially
prepared to read the pictures for each instrument, and a convenient plan is to use
a sheet of glass which has the scale ruled or etched or photographed upon one
surface, so that when the glass scale is placed in position over the photographic
print or negative, all angular deviations from the vertical and horizontal lines can.
be seen at a glance and the bearings computed by simple addition and subtraction.
For constructing a plan or map it is of course necessary in an ordinary way to.
have photographs of the same points taken from at least two different stations, when
the positions of all those points can be plotted by the ordinary method of cross
bearings, the bearings being taken from the photographs by observation and
computation. A measured base line and scale of reduction are obtained in the
ordinary way.
I have now described the ordinary procedure which I adopt when using my
instrument for mapping purposes, but the procedure may be modified to meet
special circumstances, and whenever it is necessary to work very quickly, time may
be saved by omitting to trouble about the orientation of the horizontal circle. The
photographic record is quite independent of the orientation of the horizontal circle.
aud, provided the instrument is level and the compass inside has had time to come
to rest, the photograph will bear on its face all necessary information and if any
selected point is sufficiently clearly discernible, it is not even necessary to bring the
intersection of the telescope webs upon the point, because if the camera is pointed
approximately in the right direction, the correct bearing of every discernible point
can be afterwards ascertained by measurement on the picture.
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 :-
1. The combination and arrangements of parts forming an improved instrument
for surveying with the aid of photography substantially as herein shown and
described.
2. The combination of a combined camera, internal compass and other parts
connected therewith of the character herein referred to with a horizontal wire,
hair or fibre close to the photographically sensitive surface of a prepared photo-
graphic plate or film in position for exposure in the camera substantially as herein
shown and described and for the purpose stated.
3. The combination with a combined camera and magnetic compass such as
herein referred to of an adjustable divided horizontal circle upon which the camera
rests and is pivoted concentrically substantially as herein shown and described and
for the purpose stated.
4. The combination of a combined camera and compass such as herein referred
to, a telescope adjustable in altitude mounted on said camera and an adjustable
divided horizontal circle, substantially as herein shown and described and for the
purpose stated.
5. The combination with a photographic camera of a revolvable tubular level.
mounted substantially as berein shown and described.

page_text: 6. The combination with a combined camera, compass and vertical index wire,
hair or fibre, of a horizontal hair or fibre close to the photographically sensitive
surface of a prepared photographic plate or film in position for exposure in the
camera substantially as herein shown and described and for the purpose stated.
Dated this 13th day of December 1894.
J. BRIDGES LEE,
By Harris & Mills,
23, Southampton Buildings, London, W.C., Agents.