238 



DEEP BOREHOLE SURVEYS AND PROBLEMS 



caused purposely, as by explosive charges, air and sound 

 waves are set up and these are not surface earth waves. 

 Air sound waves are distinctly indicated on the record for 

 quakes due to human agency, and they are quite distinct 

 from those movements and tremors of the earth due to 

 earth waves. These are propagated much more slowly 



I 2 3 4 5 6 16 

 Fig. 158a. — Impulse record. 



I 

 ^ V 



^S 



Speed of Recording Paper =One Inch Per Second of Time 



■Impulse record 



Fig. 158b.— {After Kithil.) 

 Fig. 158. 



than deep earth waves; consequently, although they are 

 generated at the same time, they appear later on the record 

 as will be seen in Fig. 1586. Figure 159 (after Rankine) 

 shows a gelatine shot artificial shock record. 



The new and only British seismograph instrument of the 

 Cambridge Instrument Company is an advance upon 

 Mintrop's original apparatus being more sensitive and 

 dependable. It has been evolved as a result of the Iraq 

 oil-field researches of Dr. A. 0. Rankine, Professor of Phys- 

 ics, at the Imperial College of Science and Technology.^ 

 Its advantages over other types lies in the linking device 



1 We are indebted to Dr. Rankine for Fig. 160 and the details. Sympo- 

 sium at the Institution of Mining and Metallurgy, Apr. 18, 1929; see also 

 British Patent Specification No. 17402/29. 



