PHOTOGRAPHIC METHODS 193 



bring a new piece of photographic paper strip into the 

 picture plane and by pressure on the middle button of the 

 switch box illuminate the lamp. We have now to get 

 the depth which is got from the rope or rods and in this way 

 can carry out hundreds of surveys without pulling the 

 plumbing cylinder out of the hole. A dark room is impro- 

 vised in which to develop the sensitive figures of Fig. 129. 

 The results can be evaluated by means of a polar coordinate 

 scaler or a rectangular coordinate tracer. 



Figure 132 shows an actual survey by this method of a 

 borehole with a 2.9 per cent deviation off vertical, the small 

 circles being the horizontal sections of the borehole at the 

 respective depths in meters, the axes numbers being the 

 lateral displacement in meters. 



For Haussmann's apparatus the following advantages 

 over previous devices have been made and they appear to 

 be well founded: 



1. A higher degree of accuracy is obtained with a sensi- 

 tive level than with a plumb bob or pendulum. The level 

 permits of a reading accuracy of 0.1 to 0.01 per cent. 



2. It provides a sure reading in magnetically disturbed 

 regions, giving reliable direction determinations. 



3. Repeated measurements can be made, each giving a 

 sharp photographic indication. 



4. Good centering. 



5. Simple and rapid assembling and measuring, which 

 holds also for great depths. 



Owens's Apparatus. — This is an illuminated clinometer 

 and compass device, invented by Dr. J. S. Owens in 1925, 

 and having an external and internal casing like Gallacher's 

 apparatus. The inner one bearing two corner tubes is 

 free to rotate on the long axis pivots. This, of course, 

 keeps the inner casing with the clinometer and compass 

 always swinging into the vertical and horizontal planes, 

 respectively; the other inner carrier tube holds mechanism 

 which controls the length, number and interval of expo- 

 sures. This mechanism is a clock-operated controller 

 making and breaking circuit with electric lamps. The 



