The Ely miner. [volume] (Ely, Minn.) 1895-1986, 1931-08-21

taking ordinary gelatine film and immersing Il
in a solution of kryptocyanine-
The next requisite is a special type Of filter,
so dense as TO have the opaqueness OF rubber
All lenses have to greater or less extent the
property of prism; that is. they break up the
white light into spectra. It is necessary under
given conditions to filter TO eliminate the
active colors( such as violets, blues and greens)
and restore the light TO white. By Increasing
the opaqueness of the filter more Of the visible
spectrum is eliminated, and it is possible 10
eliminate it altogether. This is what has been
done in the cast Of the long-range camera
Through its filter only the infra-red rays are
admitted, and ground haze or smoke is no
obstacle to them, objects are recorded on the
film which are invisible to the naked eye In
this way Captain Stevens was able TO photo
graph Mount Rainier from the record distance
of go miles, the peak jutting up above the
horizon, though it miles beyond IL The
peak was invisible TO the eye from a height Of
nearly $1,000 feet, owing to the haze.
In the taking Of photographs for map-making
a special technique has had to be developed.
equally applicable to military and commercial
purposes. It is not enough to sight the camera
and trip It; all sorts Of things have to be de-
termined before the photograph be taken.
Because only the center of each photograph can
be considered anything like OFFICIALLY perfect,
large number Of overlapping exposures have 10
be made
As a rule those overlapping in series must do
so by about go per cent, while those overlapping
in strips must do by about 80 per cent
Thus in flying along given line Of flight il Is
important to know the interval at which the
photographs must be taken in order to obtain
the go per cent overlappage. In the next line
of fight. parallel to the first the pilot must
obtain the so per cent overlappage by guiding
the airplane the guide points already
determined.
One instrumental reality a combination OF
four-does most of the work 1t consists Of a
ground-glass plate which a number OF
straight lines are marked At the rear end Is
a transverse black line and moving I'D and
down the plate is an aluminium marker parallel
to the black line. rheostat at the back starts
the marker moving and controls its speed, the
idea being to control the speed of the marker as
it comes down the plate toward the black line
so that objects reflected on the plate from the
ground move at the same rate When that Is
done the interval Is fixed
II the airplane is found to be Grabbing"
across the ground. the interval finder, as the
instrument is called, may be swung around so
that the photograph win be square to the strip
Of land to be photographed. This Grabbing"
can be detected accurately enough By looking
at the plate.
When all the data have been gone over a sim,
pie tumbler switch Is tripped and the camera
begins winding the film and tripping for each
exposure. This last phase is purely automatic;
the attention of the operator is concerned solely
with keeping the camera level to prevent the
exaggeration Of titan error due to the optical
axis moving away from the true vertical.
number Of thumbscrews are provided on the
camera mounting to aid in keeping the bubble
OF spirit level In center. Three seconds BE-
fore each exposure q red light glows to warn
the operator. One light is also on the pilots
dashboard to enable him to do his part In kee1-
ing the plane level, laterally and longitudinaIy
e by Western Newspaper Union