The morning news. [volume] (Savannah, Ga.) 1887-1900, 1898-04-10
SURVEYING WITH THE CAMERA.
Important Application of PhOtOgra-
ply in Canada.

VI
ply in Canada.
From the st. louis Globe-Democrat.
Something like $4,000 square miles of
the mountainous country of Western Can
ada has been surveyed with the camera
Nothing comparable to this in the way of
Photographic surveying has been accom-
plished on any such scale anywhere else
in the world
The causes of failure on the part of
many who have tried the method and
discarded it in disgust are chiefly two.
One of these is a defective knowledge in
descriptive geometry and perspective,
which are essentials of the plotting photo
graphic surveying. The other difficulty
lies in the manipulation of the photo
graphic apparatus itself and the making
the easy thing it seems, since photographs
that would be highly acceptable to the
average photographer, professional or am
ateur, might be quite useful for the pur-
pose of the surveyor. For example, the
surveyors picture, in order to be of use,
must be taken with the camera in pre-
cisely the horizontal position. fitting never
a hairs breadth in one direction or an
other; the lens he uses must be an an
astigmat, and absolutely rectilinear, that
the image may not be in the least dis
torted; and the plate must be of a special
kind, and adjusted in the camera with a
degree of nicely of which the ordinary
photographer has no conception.
Mr. Deville, who had in charge the Ca
madam work. points out in a practical
way how many of the worst difficulties
may be easily overcome. Thus the simple
device of having a net suspended between
the legs of the tripod, in which stones are
placed to steady the camera, would save
many a negative in windy weather that
now is lost through the vibration of the
instrument. And the care which is coun-
seled in determining the exact period of
proper exposure for a given plate lens
and light, even if carried out with far
less scientific precision than is here sug-
gested would enable many an amateur
who now wastes several plates for every
good negative to reverse the proportions
of failures and successes
One curious feature of the photoeranbic
surveying which the amateur world would
not care 10 follow ordinarily, but l1nowl-
edge of Which might prove of service on
occasion, is that the aerial persDective
making the distance hazy is practically
eliminated by the use of orthochronnatic
plates, which are little affected by the
blue rays, combined with the use of an
orange-colored screen in front of the
lens. The result of course, is picture
devoid of atmosphere, and hence defec-
tive from the artistic standpoint but
probably more valuable for the purposes
OF the surveyor, who very likely has
taken the picture solely to show the exact
location, altitude and contour of a dis
tant mountain
The use of these methods Of restrio+
ing the light necessitates very long ex
posure, and this in turn makes requisite
the use of plates coated on the back with
Notwithstanding material (so-called non
halation plates, else the light reflected
from the back surface of the plate would
Iog the MIN. Mr. Deville is careful to point
out mat this coating must be in ontica1
contact with the surface of the glass.
IN other words, actually painted ,1non =
me mere placing of black cloth or pa-
per against the back of the plate being Of
no service whatever. u
hen all these technical difficulties &c
Photographic surveying are made clear
II no longer seems so strange that the
he1hod mas been but slowly adoDted nv,
surveyors, even in those districts Uhera
Us advantages would be most married.
Inc surveyors who tried il usually en-
10 get any available results, and they did
hot realize that the fault lay with them
serves and not with the method