EXPLOSIVES FOR GEOPHYSICAL PROSPECTING 33 
characteristics of speed and uniformity of detonation. A slight lag 
was noted at the higher firing amperages, but this value was so small 
and so uniform as to be considered negligible in its effect on the ac- 
curacy of seismograph work. Detonators of this type were then sub- 
mitted to field trials under actual conditions of geophysical prospect- 
ing. The results obtained, which were in direct confirmation of the 
laboratory data, demonstrated that the special electric blasting cap 
would meet the requirements exacted by exploration use. 
In closing, it seems well to point out that an electric blasting cap 
must possess, in addition to proper uniformity of detonation, other 
essential qualities, namely, excellent water resistance and detonating 
power. These two features are of primary importance, in view of the 
deep, water-filled holes employed in reflecting shooting and the pre- 
viously described special seismograph gelatins which are, by virtue 
of their necessarily stiff character, less sensitive than normal powders. 
In regard to the latter point, it is considered that a composition cap, 
containing a high velocity, high strength base charge, is particularly 
adapted to geophysical prospecting. 
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