282 HISTORY OF GEOLOGY AND PAL/EON TOLOGY. 



voluminous literature now exists on earthquakes and slight 

 tremors experienced in Europe during the last quarter of the 

 nineteenth century, special commissions having been appointed 

 in most countries to keep a record of observations. 



In Great Britain, Professor James Geikie, Davison, and 

 White continue the work of R. and J. W. Mallet, and there is 

 no lack of observations in North America, Guatemala, Mexico, 

 India, Australia, and Africa. Seismological studies were initiated 

 by Dr. E. Naumann and Dr. Knipping in Japan, and the newer 

 reports of Dr. Milne, Koto, Sekiya, and others in the 

 Transactions of the Seismological Society of Japan } contain full 

 accounts of the earthquakes in these localities. 



Of late years very delicate seismometers have been 

 invented, by the use of which it has been possible to obtain 

 accurate records, not only of violent shocks but of finer 

 pulsations and tremors imperceptible to human sensation. 

 Cacciatore of Palmero used as a seismometer a shallow shell 

 filled with quicksilver, and having a number of notches at 

 regular distances round the edge; small cups were placed 

 below the notches, and in the event of any movement of the 

 shell, the quicksilver escaped into these cups and could be 

 weighed as a measure of the intensity of the shock. This 

 simple apparatus was replaced by numerous others of much 

 more complicated construction, which sometimes applied the 

 pendulum, and were sometimes made self-registering by 

 specially devised clock-work. Thanks to many ingenious 

 inventions, meteorological science now possesses a wealth of 

 observations on the frequency, continuance, periodic recur- 

 rence, and geographical distribution of earthquakes, as well as 

 on the mode of transmission, direction, intensity, rate of 

 propagation, and character of the shocks. Geologists have 

 concerned themselves more with the destructive effect, the 

 surface deformation and geological action of crust-tremors, 

 and with the modifying influence exerted by the various kinds 

 of rock upon the intensity and transmission of earth- 

 movements. 



Mallet, Von Seebach, Von Lasaulx, and Dutton proposed 

 various methods of ascertaining the area of impulses during 

 an earthquake. Both Mallet and Seebach concluded from 

 geometrical methods that the seismic focus was at a 

 comparatively small depth below the surface, but this result, so 

 far from having been confirmed, seems to be contradicted by 



