ME. MALLET Olf THE TEAHSIT-YELOCITT OE EAETHQUAKE WAVES. 657 
gotiations had to be entered on with several parties ; with the occupier of some land at 
Pen-y-Brin, about a mile to the east of the quarries, where the most suitable spot for 
placing the seismoscope (the observer’s station O, see Map) was found, for permission to 
enter his land, and level down to a horizontal surface the face of the rock, here occu- 
pying the surface of the ground, and to erect an observer’s shed over it ; and with the 
Electric Telegraph Company, for the hire of insulating telegraph poles and wires, and 
for their erection over the range interv^ening between this spot and the highest reach of 
the quarry hill. 
As these great blasts are fired only occasionally and at uncertain intervals, and being 
prepared must he fired imthout 'postponement, and within a given hour of the day, namely, 
during the workmen’s dinner hour (12 to 1 p.m.), when the quarries are clear of men, 
and therefore safe from accident, it became at once obvious that very frequent journeys, 
both on my own part and on that of such assistants as I should require, would have 
necessarily to be made to and from Holyhead ; and to economize as much as possible 
the large expenditure that must thus arise, I applied to the City of Dublin Steam 
Packet Company, and to the Chester and Holyhead Eailway Company, through their 
respective Secretaries, representing the scientific character of the undertaking, and 
requesting on their parts cooperation, by their permitting myself and my assistants, 
with any needful apparatus, to pass free to and from Holyhead by their respective 
vessels from KingstowTi Harbour. After much fruitless correspondence I regret to say 
that both these Companies refused to render any assistance whatever, a boon the refusal 
of which greatly increased the expenditure for these experiments. Lastly, I placed 
myself in communication with Messrs. Eight, the contractors of the vast works of the 
Quarries and Harbour, and in August 1856 received from them the assurance of every 
assistance that they could afibrd consistently with the prosecution of the works. To 
them, to Mr. E. L. Cousexs, C.E., the acting engineer for their Firm on the works, and 
to Mr. G. C. Dobsox, C.E., chief engineer on the work under Mr. Eexdell (since under 
Mr. Hawkshaw), my thanks are due for the best and most cordial assistance upon all 
occasions. 
The position for the observer’s station and seismoscope upon the levelled floor of rock 
at Pen-y-Brin haHng been fixed upon, the first operation necessary was to obtain an accu- 
rate section of the surface in the line between that and the quarries, a geological sec- 
tion of the rock formations along the same line, and with precision the exact distance in 
a straight line, from some fixed point adjacent to the quarries, to the observer’s station. 
The fixed point chosen at the quarries was the flagstaff at the bell, which is rung when- 
ever a blast is about to be fired, this being so placed that from it measurements and 
angular bearings with the line of range, OW (Map), from the various sites of future 
explosions could readily be made, and thus the exact distance of each focus of explosion 
(to be hereafter experimented on) from the seismoscope at O ascertained, the flagstaff 
always remaining undisturbed as a fixed terminal at the quarry end of the range. 
The whole surface, O to W, was carefully levelled over, and the distances chained, as 
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