202 REPORT— 1861. 



of stone, rubbish, and clay, conducting wires were led out to a suitable and safe 

 distance, so that on making by these the circuit complete between the poles of a 

 powerful Smee's galvanic batterj', a small piece of thin platinum wire adjusted 

 within the charge of gunpowder became heated, and ignited the powder. 

 The explosion thus followed instantaneously the making contact between the 

 poles of the battery. 



Experience has enabled the engineers charged with the work so exactly 

 to proportion the charge of powder to the work it is intended to perform in 

 each case, that no rock is thrown to any distance; the whole force is consumed 

 in dislocating and dropping down to its base as a vast sloping talus of disrupted 

 rock and stone the portion of the cliff operated on ; in fact, at the moment 

 of explosion the mass of previously solid rock seems to fall to pieces like 

 a lump of suddenly slacked quicklime. The shock or impulse, however, 

 delivered by the explosion upon the remaining solid rock, behind and around 

 the focus, and propagated through it in all directions outwards, as an elastic 

 wave of impulse, was at an early stage of the operations remarked to be so 

 powerful, that it could be felt distinctly in the quaking of the ground at 

 distances of several hundred yards, and was sufficient even to shake down 

 articles of delf ware from the shelves of cottages a long way off from the 

 quarries. 



Early in 1853 I visited those quarries, and examined generally the adja- 

 cent locality and rock formations, and having satisfied myself that these 

 operations could be made available, I applied to my distinguished friend, the 

 late lamented Mr. Rendel, C.E., the engineer-in-chief of the Asylum Harbour, 

 and readily obtained from him permission to make such experiments as should 

 not interfere with the progress of the works. 



The prosecution of these experiments having been favourably represented 

 to the British Association for the Advancement of Science, and to the Council 

 of the Royal Society, a sum of money was voted by each of these bodies 

 respectively, and placed at the author's disposal, with the desire that he should 

 undertake and conduct the experiments. 



It was not, however, until the summer of 1856 that my own avocations and 

 various preliminaries allowed any progress to be made with the experiments 

 themselves. Negotiations 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 obser- 

 ver'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 occupying the sur- 

 face 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 intervening 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 without 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 expen- 

 diture that must thus arise, I applied to the City of Dublin Steam Packet 

 Company, and to the Chester and Holyhead Railway Company, through 

 their respective Secretaries, representing the scientific character of the un- 

 dertaking, and requesting on their parts cooperation, by their permitting 

 myself and my assistants, with any needful apparatus, to pass free to and 



