82 REPORT—1850. 
jection to that which I have proposed, namely the supposed difficulty of keep- 
ing a galvanic battery constantly in action to ensure that of the seismometer. 
One would have thought that the thousands of miles of electric telegraph 
now kept in hourly activity, would have shown the groundlessness of such 
an objection. 
The observations heretofore made with seismometers, constructed on the 
solid pendulum principle, are worthless, by the nature of the instrument, even 
if they were not much too few and too ill-connected to be of any service. 
A seismometer must give the direction of emergence of the earth-wave at the 
station, the time occupied by the passage of the wave, and the form of its 
crest, ὃ. 6. its altitude and amplitude. The transit velocity at the station 
must for the present be assumed as that due to the modulus of elasticity of 
the formation upon which the instrument stands. 
Upon this subject I would refer to my memoir on a self-registering seis- 
mometer, Trans. Roy. Irish Acad. for 1846. 
It has been objected to the value of determinations of elastic moduli as 
respects our subject, that they will only give us information as to the purely 
superficial substances of the earth’s crust. This is however not a valid ob- 
jection. The Belgian coal-measures dip as far below the sea-level as Chim- 
borazo rises above it, so that it is in our power to get measures of the 
elasticity of formations extending in actual depth to ;4,. of the earth’s radius, 
and by obtaining a series of moduli for the same rock, descending in depth, 
to get the law of its variation, and so to arrive at conclusions as to rocks 
which we can never see or examine by the senses; and again, it is not phi- 
losophic to refuse to investigate to the depth we may, because we are limited 
to a certain depth; to refuse the aid, as Locke says, of the sounding-line, 
because we cannot always strike the bottom with it. 
To be truly serviceable however to the physical geologist, the elastic mo- 
dulus of any given rock should be ascertained in the three directions as it 
lies ἐγ) std, of depth, breadth, and length. Those desirous of entering more 
fully into this part of the matter, I refer to the Rev. W. Haughton’s Memoirs 
on Elastic wave Motions (Trans. Roy. Irish Acad. 1849). 
Direct experiments for admeasurement of the transit rate of elastic waves 
in the solids of the earth’s crust, and especially through its loose and inco- 
herent formations, clay, gravel, sand, &c., are of great value to this inquiry, 
and may be made by the explosion of small quantities of gunpowder in a 
suitable manner. 
These investigations, involving expensive instruments and the devotion of 
much time aud conjoint labour, can only be attempted with the aids and — 
support that bodies such as the British Association can bestow ; and probably 
no branch of cosmical science would better reward efforts judiciously made 
to advance it, a reward which would not be confined to geology, but would 
enrich many other departments of physies and natural science. 
I have now concluded the Report upon the facts of earthquakes, so far as 
time and other avocations would permit, but I do not view the subject as 
completed. 
In a second part of the present Report, therefore, I hope, with permission 
of the British Association, to present— 
ist. A complete catalogue or chronology of earthquakes from the earliest 
times to the present day, discussed with reference to time and to distri- 
bution over the earth’s surface. 
2nd. Earthquake maps founded upon this dideusaten: 
3rd. As complete a bibliography of earthquake literature as I have been 
able to collect. 
