OPTICAL METHODS OF BORE-HOLE INVESTIGATION 339 



(a) In infra-red light, details of the rock are reproduced less clearly than 

 in ordinary light; so, in infra-red light the clarity with which grains of 

 sandstone and lamination of clays (Fig. 6) are determined is less. 



(b) No additional data are detected on photographs obtained in infra-red 

 light. 



As was shown above, increasing the wavelength of the light improves the 

 transmittance a little, but the contrast is practically unchanged. Thus a large 

 effect in going to long waves in not observed. Considering what has been 

 stated above, and also that photography with infra-red rays is technically 

 more difficult, the conclusion can be reached that photography of rocks 

 along the walls of a well should be carried out in ordinary light. 



In photographing the samples a mercury-quartz lamp with a filter of Wood 

 glass was used as the source of ultra-violet rays. The photography was carried 

 out on isopanchromatic film; a yellow filter, absorbing the ultra-violet rays, 

 being placed in front of the objective lens. In connection with this, lumines- 

 cent radiation was mainly recorded on the photographs of rock samples 

 in ultra-violet rays. Photographs of rock samples exposed to ultra-violet 

 radiation indicate the presence of bitumens and their distribution through 

 the rock. Since the distribution of bitumen in the rock depends to some 

 extent on the structure of the rock, photography of bituminous rock conducted 

 in ulti'a-violet rays conveys to some extent the structure of the rock. On 

 photographs of non-bituminous (for example, extracted) rocks, the structure 

 of the rock is not shown up clearly enough. 



If the question of studying the bituminosity of rock is excluded from the 

 investigation, illumination by ultra-violet rays in photography of rocks 

 does not offer any advantages over illumination by ordinary hght in the 

 study of rocks by photographs, because, owing to wide scattering, ultra-violet 

 rays are transmitted Avorse by the drilHng fluid and possess a greater 

 capacity for loss of contrast. 



It is obvious that there is no sense in photographing rock in order to study 

 the bituminosity; for this it is sufficient to record the total intensity of 

 luminescent radiation. 



2, To find out how the position of the source of illumination affects 

 the clarity of the rock image, some rock samples were photographed with 

 illumination by direct and oblique (at an angle of 45%) rays. Comparison 

 of the photographs obtained shows that with illumination of the rock sample 

 by direct rays the photographs are "blank" (see Fig. 6); the grain of the 

 rock is more poorly defined, and the rock projections are less noticeable. 

 Therefore photography of rock should as far as possible be conducted with 

 side illumination. 



