SCIENCE AND INDUSTRY. 
regulated by the speed at which the aeroplane is travelling. The photos.. 
are taken at intervals, which correspond with a definite horizontal 
distance travelled by the plane. ‘Thus every few miles a photograph is. 
taken, and the quicker he flies the quicker the air propeller works the 
mechanism. The rate can also be altered by moving a small lever on 
a slotted scale, thus allowing for lenses of different focal lengths covering 
different lengths of country, and for variations due to changes in height. 
Simultaneously with the exposure of each section of film a tiny 
record is made on each (by means of a supplementary lens) of the 
reading of the height of the machine and of its compass bearings, so 
each negative is provided with a record of the direction of flight over 
the territory that is being photographed. There are times, however, 
when the compass behaves in a very erratic fashion during flight, and 
compass direction is not yet sufficiently reliable. An interesting story 
is told of the work of this camera during its trials at Farnborough. 
An. officer was sent to make a strip photograph of a certain stretch 
of the Thames, to show that a series of exposures could be made with- 
out gaps and without undue overlaps. When the film was developed, a 
most mysterious blurring of three or four pictures was found, as well 
as one or two negatives entirely blank. After much investigation and 
theorizing as to the cause, it was eventually found out by the admission 
of the pilot that he was the cause, as he had looped the loop, just to 
see how it looked on paper. . 
The method of fixing the camera in the plane may vary. Many 
distortions are introduced into aerographs by the inclination of the axis 
of the lens, by the changing contour of the land, and slight alterations in 
height of the aeroplane. Such errors must be corrected before using 
the pictures for map making. Experiments have been made with 
gimbal rings and dash pots to give the camera the movements of a 
damped pendulum, so as to secure it always in a vertical position, and 
free as possible from vibration. The results have not been sufficiently 
satisfactory. Mertie and others in the United States of America have 
used a camera mounted as a pendulum, controlled by a gyroscope, and 
results have been encouraging. Deviations up to 2° from the vertical 
were given, and this is too great an error to permit of uniformly good 
register between adjoining negatives. Better results are hoped for, 
especially from a more stable type of aeroplane than the one they used 
(J.N-4-type Curtiss). 
Tyres or Maps—anp Oonrror Ports. 
Maps are made to many different scales, and there are many 
varieties, such as plan maps showing natural and cultural features, 
and relief maps showing, by contour lines or other means, the 
regional relief. The general topographical map includes most of these 
features, but vary in scale—the United States of America being com- 
monly 1 in 250,000 to 1 in 62,500, while the British seale is 1 inch = 
1 mile. : 
Series of aerographs fitted together do not constitute a true map. 
There may be errors due to distortion, to different scale photos., and 
lack of geodetic control. Even when all the photos. have been brought 
to the same scale, and distortion corrected, an accurate map requires 
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