1898-99.] Prof. Knott on Earthquake Vibrations. 
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The Propagation of Earthquake Vibrations through the 
Earth. By Professor C. G-. Knott, D.Sc. 
Address delivered at the request of the Council, July 10, 1899. 
{Abstract.) 
The history of seismological research and discovery may be con- 
veniently divided into three great epochs. 1. We have the 
recording of earthquakes in the popular significance of the term, 
with an enquiry into their character, based almost entirely upon 
the (usually) destructive results of their visitation. 2. We find 
investigators beginning to appeal to experiment to elucidate some 
of the effects noticed, with a growing appreciation of the necessity 
of recording all palpable earthquakes, whether destructive or not. 
One of the most honoured names in this connection is that of 
Mallet, whose two volumes on “ The Great Neapolitan Earth- 
quake ” form a classic in the literature of the subject. Most of 
the developments of recent times will be found in embryo in the 
pages of this monumental work. 3. The introduction of instru- 
ments for recording earthquakes, and, as a natural consequence, the 
recognition of pulsations and tremors and the various kinds of 
earthquake too feeble to be detected by our senses. 
At every stage in this history, geological and physical problems 
of intrinsic difficulty have been encountered; and it is to the 
discussion of some of the most recent of these that this address is 
devoted. 
From the days of Mallet and Hopkins, numerous reports on 
earthquakes and seismological phenomena have been prepared and 
published by the British Association ; and the last of these, from 
the industrious pen of J. Milne, F.R.S., formerly Professor of 
Mining in the Imperial University of Japan, has a surpassing 
wealth of detailed facts and of suggested theories. And yet, 
before this report was issued in printed form, the careful scrutiny 
of tremor records had led Professor Milne to the evolution of an 
