Spirit of the age. [volume] (Woodstock, Vt.) 1845-1913, 1898-10-01
PHOTOGRAPHIC SURVEYING.


Ono of the Important Use, to which the
Camera Has Eeen Pint
Something like 80 GEO square miles
of the mountainous country of west
ern Canada has been surveyed with
the camera Nothing nuarabh
to this Ill the way Of photographic
surveying has been accom- lished
on any such scale anywhere else in
the world &C.,.
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 defect
i've knowledge in descriptive geom-
etry and perspective, which are es-
sentials of the plotting Photographic
surveying. The other officially les
in the manipulation of the photo
graphic apparatus itself and the
making of Il proper negative. This
is by no means the easy thing it
seems, since photographs that would
be highly acceptable to the average
photographers, professional or anna
teur, might be quite useless for the
purpose Of the surveyor. For exam
pie, the surveyors picture in order
to be of use, must be taken with the
camera in precisely TIE horizontal
position, fitting never hair
breadth in one direction or another;
the lens he lr>.as must be an nnastig
mat and absolutely rectilinear, that
the image may not Ire in the least
distorted and the plate must be of
special kind and adjusted i'll the
camera with Il degree of nicely of
which the ordinary photographer
has no conception.
Mr.. Deville, who had in charge
the Canadian work, points out i'll IL
practical way how muny of the
worst difficulties may be easily over
come. Thus the simple device of
having 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 instru-
ment And the care which is coun-
sclcd in determining the exact peri
oil OF proper exposure for given
plato, lens and light, even if carried
out with far less scientific precision
than is here suggested, would enable
many an amateur who now wastes
sev eral plates for every good mega
tive to reverse the proportions of
failures and SUCCESSES.
One curious feature Of tho photo
graphic surveying, which TIE anna
teur would not care to follow ord.
narily, but IL knowledge OF which
might prove of service 90 occasion,
il that the aerial perspective, max
ing the distance hazy, is practically
eliminated Gy the use of orthochro-
matte plates, which are little affect
ed W the blue rays, combined with
the uso of al orange coluFcd screen
in front Of lie lens. The result, of
course, is IL picture devoid Of atmos-
phere, and hence defective from the
artistic standpoint, but probably
more valuable tor the purposes of
the surveyor, who vely likely has
taken the picture solely to show the
exact location, altitude and contour
of distant mountain.
The use ct these methods of re-
stricting the light nGcessitates very
long exposure, and this in turn
makes requisite the use of plates
coated on the back with 4 light alb
sorbing material ESQ called nonhnlu-
ton plates), else the light reflected
from the back surface of the plate
would fog the film Mr.. Devilla is
careful to point out that this coating
must lie in optical contact with the
surfaceOf the glass--in other words,
actually painted upon it, the mere
placing of black cloth or paper
against the back of tho plate being
of no service whatever.
Wher all these technical difficult.
ties of Photographic surveying are
made clear, it no longer seems so
strange that the methed has been
but slowly adopted by surveyors,
even in those districts whore its ad.
vantages would be most marked.
The surveyors who tried it usually
failed to get any available results,
ana they did not realize that the
fault lay with themselves and not
with the method st. Louis Globe.
Democrat.