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Canadian Forestry Journal, January, 1919 



be made to occur in two photographs. What is 

 then done is to cut out the part in each photo- 

 graph containing the point and paste the two 

 photographs alongside each other, on the usual 

 stereoscopic card. Here it is necessary to get 

 the positions of the two photographs by experi- 

 ments, as for certain optical reasons, unknown 

 to me, if you put one photograph on the right 

 whereas it should be on the left, the proper effect 

 of height and depth is reversed, although the 

 two photographs may look identical. However, 

 once this is successfully done the combination 

 of the photographs can be used in the usual 

 stereoscope and a very good idea of the proper 

 perspective obtamed. 



Effects of Stereoscope. 



Another interesting point is that two different 

 photographs giving, for instance, a fuzzy ap- 

 pearance singly can, by viewing stereoscopically, 

 be made to give a very good single image. 



Using this method, it is possible to very 

 closely examine positions on the ground, and in 

 case of batteries I know it is possible to tell 

 whether emplacements are made of concrete or 

 of sand bags. This method obviously offers 

 chances of value in the examination of items on 

 the ground which, from a survey point of view, 

 special information is required about. 



Before coming over here I was stationed at 

 Dunkirk for the last year, where a great deal of 

 aerial photography was done over places such 

 as Bruges, Ostend, etc., where the Archies were 

 severer probably than anywhere else in the 

 world. 



Survey Photography. 



To continue now with aerial photography, as 

 applied to survey work. 



When I came over here, I knew practically 

 nothing about survey work. I gather now that 

 photography plays a considerable part in survey 

 work over mountainous country, and that expe- 

 ditions set out in summer months in order to 

 photograph ranges of mountains from known 

 positions with the idea of getting the heights 

 and positions of the mountains. I have seen 

 some of these photographs taken by the Geodetic 

 Survey and have admired them immensely, but 

 looking at them it struck me that when you 

 photograph a mountain there must be various 

 foothills and minor mountains leading up to the 

 main peak and that photographs taken from one 

 point will not give any idea of what lies be- 

 tween these foothills and the mountain itself nor 

 of what lies behind the mountain. I suppose to 

 obtain particulars of these it is necessary for a 



party to go round to another point, at a different 

 angle to the original, and to make another set 

 of photographs from there. This further ex- 

 pedition is naturally a matter of time, and I 

 think it possible that aerial photography may be 

 able to make much of this unnecessary. The 

 machines, working in conjunction with a sur- 

 veying party and in touch with them by wireless 

 telegraphy or wireless telephony, could receive 

 orders to fly over any particular portion of the 

 mountain and take such photographs as are 

 required. For instance, a photograph taken 

 immediately over the top of a mountain will 

 show the general contour of the mountain and all 

 its couloirs and surrounding peaks. It will give 

 no idea of the altitude of the mountain, but it 

 will certainly show a great deal which a photo- 

 graph taken from some known point opposite 

 will not show, such as the configuration of the 

 snow fields round the peaks, the distance be- 

 tween individual peaks, and possibly such a 

 photograph might give a good indication of the 

 best method of climbing the peak, if this is 

 required. 



Mapping Rivers and Lakes. 

 To get away for a moment from mountain 

 work, aerial photography could give very valu- 

 able results in the mapping out of rivers and 

 lakes. These particular objects are especially 

 adapted to aerial photography, as it is possible 

 to obtain in one photograph the shape of an 

 entire lake, and a series of photographs of a 

 river will give the course of a river. Without 

 knowing anything about mapping out rivers and 

 lakes, I imagine it must be a case of covering 

 most of the water in boats and fixing numerous 

 positions along the shores by means of triangula- 

 tion, so that in this case an aerial photograph 

 might be able to dispense with many days of 

 work. Photographs taken over water would 

 also, to a great extent, show the configuration 

 of the bottom, so that unless precise details were 

 required, the necessity of taking soundings 

 could be obviated. 



Life of Aeroplanes. 

 Many people, without stopping to think, are 

 of the opinion that for the purposes of flying 

 all that is needed is a good looking machine, a 

 pilot, and one mechanic. If one went by the 

 papers one would be apt to think that all that 

 has to be done is for the pilot to step into the 

 machine, the mechanic to give the propeller a 

 twist, and off the machine goes. As a matter 

 of fact, this part of flying is only a very small 

 item, and it should not be necessary for me to 

 say that the whole success or otherwise of sue- 



