214 REPORT — 1861. 



of 0"'0566, or very nearly 0"-06 for the time of hang-fire, which can be 

 viewed, however, only as an approximation. It must vary slightly with 

 every diflPerent " heading," depending as it does upon a great variety of con- 

 ditions, but probably much more upon the exact proportion subsisting in any 

 given case between the actual resistance of the rock to the powder employed, 

 than upon the absolute quantity of the latter, although the total mass of 

 powder burnt is also an element. The greatest observed difference between 

 the greatest and least hang-fire amounted to 0"*03, which, converted into 

 distance at the mean transit-rate of our experiments, would give a. possible 

 maximum error due to this cause of about 31 feet per second. The probable 

 error cannot be more than about one-half that amount. This correction, 

 converted into distance, is also additive. 



By the methods thus described the experiments were commenced and 

 conducted up to the middle of 1857; great trouble and difficulty, however, 

 were experienced from the outset in keeping the arrangements in working 

 order, and so as to be efficient when wanted at the very brief notice that 

 could be afforded me beforehand by the officers in charge of the works, 

 when suitable headings were about to be fixed. The entire line of telegraph 

 wires, the observer's shed, &c., were exposed to mischief and depredation, 

 and to injury in that tempestuous place by storms, &c. The long intervals 

 between the experiments involved preparations and adjustment of every part 

 of the galvanic apparatus afresh upon each occasion ; and for the most trifling 

 repairs workmen had to be brought from Conway, or even from Manchester, 

 as also, in every case, to make good the branch-conductors from the tele- 

 graph wires. The length of the range and hilly character of the ground 

 also produced much difficulty in being assured that all was right from end 

 to end against the moment at which the firing was obligatory, as well as 

 great personal fatigue at a moment when composed ease and freedom from 

 fatigue were most desirable for good observation. 



These difficulties, in great part foreseen, had early caused me to turn 

 my attention to the practicability of so adjusting at the observing-station a 

 telescope of large field and clear definition, and so disposing the Grove's 

 firing-battery and other apparatus at the quarry clifi", that all could be clearly 

 seen from the former point, and the act of making contact at the firing- 

 battery observed by myself with distinctness and certainty, the two extre- 

 mities of the range being thus, as it were, visually brought together. 



Two attempts to experiment in the summer and autumn of 1857, ren- 

 dered abortive by derangements of the galvanic apparatus, caused me finally 

 to abandon it, though unwillingly. I found, however, with some satisfaction, 

 that, subject to the possible fatality of a cloud settling over the quarry clifi', 

 and so shutting it out from sight just at the critical moment, the telescopic 

 arrangement, on trial, really seemed to offer quite as accurate results as the 

 more complex method, and more difficult to manage, of galvanic contact- 

 making ; and the new mode was thus continued to the end of the experiments. 

 The firing-battery being so disposed upon the sloping brow of the quarry cliff 

 facing my station as to be clearly visible to me, as well as every movement 

 of those employed there, a code of signals was arranged between myself 

 and Mr. Cousens, by which we should mutually become cognizant of the 

 state of preparation, &c., and successive acts at our respective stations. When 

 all was ready at both ends for the explosion, the final signal was made by 

 INIr. Cousens, by elevating a bright red flag (mounted upon a short and 

 light staff') to a vertical position, the lower end resting on a fixed point; a 

 prearranged interval of a few seconds (usually 10") intervened, when he 

 dropped the red flag, rotating it upon the loAver end of the staff held in the 



