June io, 1920] 



NATURE 



457 



Aircraft Photography in the Service of Science. 



By H. Hamshaw Thomas. 



\ IRCRAFT photography as developed during | The contrast between the wadi forms produced 

 -^^ the war possesses great potentialities as an I in these lacustrine or alluvial deposits and those 

 instrument of scientific research. The value of | carved out of the adjacent Cretaceous rocks is 



the aeroplane in geographical and g"eological 

 exploration has already been emphasised in these 

 pag-es, and its employment in the reconnaissance 

 of little-known countries need not be further men- 

 tioned ; but if aeroplane exploration is valuable, 

 its worth is greatly enhanced by systematic 

 photographic work. For, while a trained observer 

 notices many features, it is quite impossible for 

 him to observe and note more than the salient 

 points seen from a swiftly flying machine, while 

 the camera instantly records every feature in the 

 field of view. Again, from a safe height of, say, 

 10,000 ft. only the larger elevations or depres- 

 sions are visible to the human eye, but if paired 

 photographs are taken for the purpose of stereo- 

 scopic examination with a uide base of, perhaps, 

 500 yards, then the whole of the ground relief 

 becomes visible in a most striking manner. But 

 not only do photographs provide a means of 

 obtaining and recording information ; they also 

 show the relative positions of objects, and, if 

 taken on an organised system, provide a 

 topographical survey for use in map construction.' 

 In addition, I was frequently struck with the 

 value for scientific purposes of material obtained 

 in the course of the R.A.F. work in Egypt and 

 Palestine, and the purpose of this article is to 

 indicate some types of information which may 

 be furnished. 



Air photographs may serve either as useful 

 illustrations of known scientific facts, or as a 

 m.eans of discovering new facts, and while they 

 are mainly of geographical or geological interest, 

 they may also assist the botanist, archaeologist, 

 and meteorologist. 



Geography and Geology. — As examples of the 

 illustration of known facts, we may mention the 

 remarkable photographs of Vesuvius taken by 

 Group Capt. A. E. Borton, C.M.G. One of 

 these has already been published in the Press, 

 and it would not be easy to find a more striking 

 demonstration of the structure of a volcanic cone. 

 Among the photographs taken in Palestine wo 

 had many good illustrations of erosion and river 

 development. The soft lake-beds of the Jordan 

 valley were shown in the process of weathering 

 out to form what the Americans term "bad-land 

 topography." In this region marls and clays 

 which have been baked by the hot, rainless 

 summer are denuded at a great rate by the heavy 

 winter rains, and give rise to a complex system 

 of steep-sided wadis spreading back from the 

 main drainage channels. The sides of these wadis 

 are bare of vegetation, but their bottoms become 

 filled with scrub when reduced to the base level 

 of erosion. 



1 See Cenginphical Journal, May, iqjo. 



NO. 2641, VOL. 105] 



very noticeable, and we have also illustrations of 

 the different erosion forms produced on steep or 

 gentle slopes.- 



The River Jordan, which had never been very 

 accurately surveyed before the war, has now 

 been photographed over a considerable distance, 

 and furnishes striking examples of some of the 

 phenomena of river development. In its lower 

 part it has cut down a distinct and well-marked 

 meander-belt below the level of the surface of the 

 lake-beds of the old valley. The river is con- 

 stantly changing its course in this belt (see Fig. i), 

 which in most places is well covered with vegeta- 



,. I. — Meander belt of the River Jordan north of Jericho, showing the 

 formation of an "ox-bow " and the cusp-shaped terraces. The dark 

 area near the stream is the belt of willow scrub. 



tion, and the old courses of the stream are often 

 plainly visible where the vegetation has not yet 

 had time to colonise the former river-bed. We see 

 " ox-bows " and loops of the river in all stages of 

 development, while sometimes a heavy spring 

 flood appears to have resulted in the stream taking 

 an entirely new course. At the sides of the flood- 

 plain cusp-like terraces often show the stages 

 in the cutting down of the gorge, while the 

 presence of hard beds may produce nodes in the 

 series of meanders. 



The illustrations of such features as have been 

 mentioned are often so striking and convincing 

 that they would be valuable to teachers and 

 students if they could be made available. 



But by the study of photographs and the maps 



