Canadian Forestry Journal, January, 1919 



21 



military lines and made several records, such as 

 a duration flight lasting twenty-four hours. The 

 British and French were not much behmd, but 

 they never tackled the problem as methodically 

 as the Germans did. 



Aerial Photography. 



As far as I know, nothing much was ever done 

 about aerial photography before the war, the 

 only aerial photographs that were taken prob- 

 ably being more or less amateur efforts with 

 kodaks. When war broke out, everyone had to 

 start in to try to develop aviation as quickly as 

 possible. There is no need for me to tell you 

 what progress has been made during the war 

 as you know already. In every paper you see 

 records of the extraordinary feats that are done 

 nowadays. 



Military Necessity. 



One point I would like to emphasize is that 

 during the four years of war all this progress has 

 been made along military lines, and machines 

 have been developed to obtain high military 

 efficiency, consisting of very high climbing pow- 

 ers, very high speed, and abilities to maintain 

 this speed at very great altitude. 



Now that hostilities have ceased, I think we 

 shall see progress just as rapid, or very nearly 

 so, as during times of war; but machines will 

 be developed along slightly different lines. The 

 doing away with the necessity of carrying ma- 

 chine guns, ammunition, bombs, etc., as well 

 as the necessity for very rapid climbing powers 

 will give machines even more excess power than 

 they possess today, thus allowing the engines to 

 be run more throttled down and, in consequence, 

 improving their reliability and their life — at- 

 tention will be turned to developing much 

 slower landing speeds than are now possible, 

 which is a most important desideratum, and 

 other advantages, such as increased stability, 

 will result. 



Commercial Uses. 



With tha application of aviation to commer- 

 cial purposes, I think machines will tend to 

 sprcialize for the various jobs they will be 

 called upon to perform. For instance, machines 

 intended for mail carrying purposes will still 

 have to possess a high speed; machines intended 

 for passengers or goods will sacrifice a certain 

 amount of their high speed for big weight lifting 

 capacities. 



The particular thing I am supposed to be hero 

 tonight to t:\lk about fits in very well with the 

 machines as they exist at the present time. As 

 you know, it was the custom on all fronts to 

 make complete and detailed maps by aerial 



photography of all trench systems, as well as 

 items of interest in the back areas, such as aero- 

 dromes, etc. Aerial photography has progressed 

 out of all knowledge during the war, and the 

 most marvellous photographs are now obtainable 

 from very great heights. 



Snapping From 20,000 Feet. 



At the beginning of the war, machines used to 

 sally forth with what would now be considered 

 an obsolete camera and take fairly good photo- 

 graphs from low altitudes. As the efficiency of 

 the anti-aircraft defences increased, machines 

 were driven higher and higher, to escape being 

 hit, and in consequence the efficiency of the 

 cameras to be used had to be increased in pro- 

 portion. Nowadays, photographs are usually 

 taken from some height not below 15,000 feet, 

 and in most cases the height of photographic 

 work is in the neighbourhood of 20,000 or more 

 feet Cameras used for this purpose have a focal 

 lens of about AYi feet and cover a plate 10 by 

 8 inches. I believe I am right in saying that 

 the photograph taken includes about six square 

 miles of country. The actual cameras them- 

 selves are comparatively simple looking arrange- 

 ments containing a high class, wide angled lens, 

 a focal plain shutter, and some form of plate 

 changing apparatus. The early cameras used 

 the Mackenzie Wishart system, but the manual 

 operation required to work this, under conditions 

 of extreme cold and attention to other necessary 

 duties, such as defence against enemy aircraft, 

 soon produced the more simple changing box 

 which is quite workable with heavily gloved 

 hands and which is capable of carrying fifty to 

 one hundred plates in one lot. 



Overlapping Pictures. 



When taking a scries of photographs, they are 

 usually taken at fixed intervals of time, accord- 

 ing to the speed of the machine and the number 

 of plates carried. In all cases, however, they 

 are taken so that each photograph alorjg a 

 certain line overlaps with the one before it and 

 the one after. When one comes to join them 

 together one merely has to pick out a landmark 

 occurring in any two photographs, superimpose 

 it. get the bearings of the photographs and any 

 lines that may be on the photographs coinciding. 



In addition, however, to those composite 

 photographs, aerial photigraphy is used very 

 largely from the stereoscopic point of view. By 

 this I do not mean to say that actual stereoscopic 

 cameras are used: but. to take an instance, sup- 

 pose you are flying along a line in which a 

 particular point occurs, of which detailed infor- 

 mation is required. This particular point can 



