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(11) 
needed. Over 33,000 line miles (53,000 km) of ground profiles have been 
obtained with this new technique. Various sources of error have been dealt 
with and at its present state of development the relative elevations of water 
surfaces may be established to an accuracy of about 20 ft. (6 m) and of land 
features within 50 ft. (15 m) over flight lines as long as 450 miles (750 km). 
Experiments with the aim of improving the accuracy of this profile recorder are 
proceeding under the direction of a sub-committee of the Surveys Research 
Committee in the expectation that the instrument can be developed to the 
extent that it will be used in connection with larger scale mapping. 
All hypsometric methods are, of course, limited by the precision to which 
observations of the atmospheric pressure at the aircraft location can yield its 
true height above datum, or at least can permit satisfactory interpolations to 
be made between widely separated datum elevations. 
PHOTOGRAPHIC FLYING 
The aeroplane made the development of vast areas in Canada possible, 
and, conversely, in the period following World War I, the challenge of rich 
unexplored lands accelerated aviation progress in Canada to a rate beyond what 
might have been regarded as normal. The use of aircraft for photographic 
surveying in the country is a fascinating history in itself. 
The original craft employed by the Air Board and later by the R.C.A.F. 
were surplus from the war just concluded, and the lack of aerodromes, especially 
adjacent to the areas of exploration requirements, quickly resulted in activities 
being transferred entirely to flying boats. Some early experiments were carried 
out with the Curtis H. S. 2L boat, but this was soon replaced by the Vickers 
Viking (Fig. A). These relatively low-speed machines had a ceiling of about 
5,000 ft. (1,500 m), but could “land” on quite small bodies of water. The 
maximum length of a photographic flight was 225 miles (350 km) and, for safety 
reasons, orders were issued that the distance from lakes or rivers suitable for 
landing must not exceed one mile (1.6 km) for each 1,000 ft. (300 m) of altitude. 
In the flying boats (with ‘pusher’ type propulsion) the photographer stood up 
in the forward cockpit exposed to the wind, and made oblique exposures forward 
and at about 45° to each side in turn. The camera was supported for this purpose 
on a horizontal track. 
The Viking did much good work. Its mahogany hull in time absorbed 
water and became heavier, leading to a deterioration in performance, but it was 
the aircraft on which the foundations of Canadian photographic technique were 
built, and some present-day senior officers of the R.C.A.F. learned much about 
Canada’s then unexplored territory from the controls of a Viking. 
It was superseded by the Vedette, which was smaller and more efficient. 
So far as can be ascertained, the Vedette was the first flying boat in which a 
vertical camera could be mounted inboard. A section of the hull, under the 
forward cockpit, was like a glorified drain plug. Once the aircraft was clear of 
the water a locking wheel was unscrewed and a section of the hull lifted clear.