8 I. DEGOLV ER 
beach and attempted to determine the velocity of the transit of 
elastic waves through sand; at Dalkey Island, velocity in granite. 
He'used a battery circuit for firing black powder, buried half a mile 
distant from the observers station, and recorded with chronographs 
at each end of the line. The arrivals of waves through the earth were 
detected by using a crude seismoscope or seismograph consisting 
essentially of a tray of mercury from the surface of which was reflected 
a spot image kept under observation through a small telescope by 
the observer. Disturbance of the mercury by earth movement de- 
stroyed the reflected image.’ 
In 1850, similar observations were made for granite on Dalkey 
Island over a distance of 1,166 feet. 
The results of these experiments were to determine a velocity of 
transit through sand of 824 feet per second and through granite of 
1,306 and 1,664 feet per second. 
In 1856 Mallet carried on similar experiments in government 
quarries at Holyhead in North Wales, determining similar velocities 
for quartz and slate (metamorphics) of 1,088 feet per second.* 
The rock velocities observed by Mallet are all extremely low and 
it is practically certain that he was observing the surface or Rayleigh 
wave. It is remarkable, however, that in his experiments he was doing 
essentially what the geophysicist engaged in refraction work does 
today i.e., discharge an explosive and attempt to determine the time 
of transit of waves generated by the explosion’ to points a measured 
distance away. It is a tribute to his genius that he had so clear a 
conception of the value of the method as a geologic tool. 
On April 2, 1914, Reginald Fessenden filed the original Sonic 
Sounder application for determining ocean depths, the first and a 
clear use of the reflection method. The U. S. Hydrographic Bulletin 
for May 13, 1914, gives an account of the location of an iceberg off 
the Newfoundland Banks, at a distance of two and one-half miles, 
by acoustic methods and on January 15, 1917, Fessenden filed his 
patent application on Methods and Apparatus for Locating Ore 
3 An exceedingly detailed account of these observations is given in Second Report 
on the Facts of Earthquake Phenomena, Brit. Assoc. for the Advancement of Science, 
Report of Meetings, 1851, Vol. 21, pp. 272-320. 
4 Account of Experiments made at Holyhead (North Wales) to Ascertain the 
Transit-Velocity of Waves, Analogous to Earthquake Waves Through the Local Rock 
Formations. Phil. Trans. Royal Soc. of London, Vol. 151, Part 3, pp. 655-679, London, 
1861. 
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