370 
REPORT- 1854. 
Report of the Committee on Earthquakes, with their Proceedings 
respecting Seismometers constructed under the superintendence oj 
Major James, R.E. By Col. Portlock, R.E., F.R.S. 
It is necessary to precede the brief statement which I am about to make, liy 
an equally brief notice of the object which, in the present case, the Com¬ 
mittee desired to attain, and of the circumstances which had given rise to it 
In 1848, at the Swansea Meeting, I brought under the notice of the Com¬ 
mittee of Section A. the importance of observing and recording the earth¬ 
quake shocks which are so frequent in the Ionian Islands, and the probabiliir 
that the Board of Ordnance would be disposed to assist in such an under¬ 
taking, if applied to by the Association; by directing some of the many 
scientific officers of Artillery and Engineers stationed in the islands torak< 
the inquiries, and by furnishing them with instruments for the purpose. As 
at that time Mr. .Mallet was engaged in devising the best mode of making 
such observations, the Committee thought it prudent to defer such an appi 
cation until the result of his experiments had been made known. T tC 
valuable Reports of that most able investigator of earthquake phcenomeni 
were presented to the Association ; but as uo definite result had been arrive 
at in respect to instruments, I again brought the matter forward in isl¬ 
and Colonel Sabine and myself were directed to communicate with 
Master-General of the Ordnance on the subject. Col. Sabine accordingly 
wrote to the Master^General, and alter consulting Sir J. Burgoyne, Major 
James, who had been entrusted with the superintendence of meteorology 
instruments, was directed to have a pair of Seismometers constructed. tU 
they might be sent to the Ionian Islands. In 1S53 the Earthquake Cod* 
mitten was re-established* and I was requested to act as the organ of inter* 
communication, in order to offer any necessary suggestions in respect to w 
construction of such instruments;—but I must turn for a moment from diesa 
proceedings to the object to be attained. 
Of the ultimate cause of earthquakes we can only conjecture; but, whether 
the result of some impulsive action consequent on the sudden developm^ 1 
ol gaseous matter, or of vapour in a state of high elastic tension, or of 
other source of pressure, causing the disruption or rending of the earm-' 
strata, it seems now generally admitted that thev are waves of vibra^ 1 - 
transmitted through the earth’s crust from the focus of disturbance, 
t/iey may be expected to he transmitted in all directions, though tbc cur; 
o the wave may be modified by many circumstances, depending on A* f ‘ 
ferent conditions, as to elasticity, of the transmitting medium ; and will ^ 
ai ive at the earths surface in such a manner, that the curve of the* 8 ,” 
* e cupve . of tl,e ewtlfs surface at ancles varying with t • 
JJnii.f nf ?! tl v UJt ™ :C,inn as regards the centre of the wave curve. At w. 
tl^v fnr 16 ? , ,nt ^ r,ioD * the remaining force of the last vibration 
-ral wrtTi ,fl!!S Jn , il directJo11 Which may be resolved into two loro 
were on fh *other tangentialthe latter being progressive. *• 
propoiL ,1 ' 8 SU . rf “ ce ’ The progressive component will increase 
surface at a morn' ,'?- rtlCa ’ ^cording as the wave intersects the * r V 
niate the nmnoH ob K UC an S ,e > anU «*• md;m that it is essential to - 
estimate the v' between *hese elements in order to determine, or at lea-’ 
SMwo modl' n - ? f t W foen » of disturbance. In order to effect tie 
wave itself as o\hl| , "^| lt ,e . ^"SS^ted : namely, 1st. To measure these"" 
both vertically and i 1 ?** * ,e f - art,1 ’ s surface by the amount of displacin' 
Jori eliSc , late ™ n Y; 2ndly. The transmission of the wave into* 1 
more elastic substance, and receiving from it the final shock so as to deter- 
