SCIENCE AND INDUSTRY. 
Reiter anp Contour Liners, 
In regions of very low relief the corrected aerophoto. approximates 
very closely to an accurate plan map. But if the pictures are taken in 
a region of moderate relief the result is not a true plan map, because of 
distortion caused by the relief itself. This has not been corrected in the 
transformation camera. Olerc, however, has dévised methods for the 
estimation of the height of objects by the measurement of their cast 
shadows in aerial photos., so that contours can be readily inserted in the 
chart. Over wooded areas it is practically impossible to show contours. 
This is a disadvantage in forest survey work. Yet the limits of wood- 
lands and types of woodland can-be determined from the photographs. 
Promising results have been obtained by the use of stereophotography, 
particularly by the use of an instrument known as the stereo-comparator. 
lt may be seen, then, that photographic surveying from aeroplanes is 
practicable and accurate to a very large degree. Although there are 
some large problems to be solved, much has been accomplished in a few 
short years, and very much valuable work could now be done with such 
speed and accuracy that was not dreamt of before the war. 
Ravin ann Enormous DrveLopmMent or AEROPHOTOGRAPHY. 
When we consider that the whole of this development has practically 
taken place in three years, and the enormous extent to which aerial 
photography was applied at the time of the armistice, it is quite reason- 
able to hope that the remaining difficulties in the practical application 
to topographical surveying will be soon overcome, and that the extensive 
facilities for war work will be utilized in the peaceful mapping of the 
world. The first aerophotos. used by the British Forces were supplied 
by the French in February, 1915. They were of an area about to be 
attacked by the British. When their value was fully realized, it is to 
their credit that their previous lack of encouragement was changed into 
a policy of rapid development. Within a week the first special camera 
for aerial work was designed, made, and delivered in France, and the 
photographic section commenced with a force of two lieutenants and a 
sergeant. 
During the last year of the war 6,500,000 prints were made for the 
Royal Air Force. In one case, just before an attack in August, 1918, 
one section alone produced 23,000 full plate photographs in 36 hours. 
Owing to the accuracy of aerophotography, the British photographed 
practically every acre of ground from Arras to the sea, and up to 50 miles 
behind the German line. It was by the aid of photography that accurate 
shooting from the aeroplane was taught. The shooter operated: 
a camera just like firing a Lewis machine gun. This Hythe Mark III. 
gun camera recorded his hits on a travelling film, and also recorded the 
exact time. If a hit was scored, a picture of the aeroplane was recorded 
in a clock dial form. 
Tratntinc or Men AND IyTreRPRETATION or AERDPHOTOS. 
The training in the School of Aerial Photography, which had grown 
to quite an institution with the Forces, is very extensive. It includes— 
besides a thorough knowledge of the various types of cameras and their 
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