294 REPORT — 1851. 



I now proceed to record the results of the experiments made as to this 

 ttTTie of hang fire, viz. the whole time from the moment of making contact 

 with the firing battery to that of the explosion, as seen by the person firing ; 

 experiments being made both by firing primings only, as figured and de- 

 scribed at page 277, and by primings and service charges of 25 lbs. of powder 

 together. 



The preceding table gives the results obtained by firing on each occasion 

 of experiment a certain number of priming cartridges only, just after the 

 service charges or mines, and hence with the batteries in as nearly as pos- 

 sible the same condition, and noting the time of burning of these by means 

 of the chronograph. 



Dividing each sum by the number of experiments, we get the following 

 averages : — 



2"'5554!l2 



A. =0"'31 94-27= average time of hang fire service charges. 



8 



1 "'882395 



B. =0"*268914=average time of hang fire primings only. 



C. 0"'362253_Q„.Qg^>.5l =average difierences. 



And deducting B from A, we find the average time for the explosion of 25 lbs. 

 of powder, as fired under our conditions, was — 



0"-3 19427 

 0"-2689I4< 



0""050513=time of explosion, 



which is a little more than -j-^odths, or about J^th of a second. 



I shall reserve such considerations as these experiments suggest until a 

 subsequent period, when about to apply the several corrections to both 

 classes of our experiments, and now proceed to describe the operations of 

 the second series of 



Experiments made in the Granite. 



The experiments in the sand at Killiney being completed, a position was 

 looked for to conduct those proposed to be made in the granite rock. After 

 examining various possible ranges about Killiney Hills, &c., the Island of 

 Dalkey was chosen as upon the whole the best locality presented. 



This island is altogether of massive granite, very uniform in texture. The 

 granite of which Killiney Hills and a large tract to the north-west, together 

 with Dalkey Island, and seaward to the Mugglins Rocks, consist, is in mass 

 of various tints of yellowish-white passing into grey. It is not quite so hard 

 as Peterhead granite, sometimes found porphyritic, with large crystals of 

 felspar, but more usually in a pretty equally difi'used mass of rather fine grain, 

 consisting of crystals of quartz, felspar and mica, often to a considerable ex- 

 tent replaced by schorl; solid masses present in working little "grain" or 

 tendency to split more easily in one direction than another. It parts from 

 the quarry usually in masses of an irregular trapezoidal form, averaging 

 from 4? to 7 feet across ; but solid blocks are easily got of eight times this 

 mass. It is much intersected with quartz veins of various successive epochs, 

 usually thin and perfectly adherent to their walls. The commoner imbedded 

 minerals are — black schorl, garnet, killinite, spodumene, and more rarely 

 apatite, beryl and fluorspar ; some few others are much rarer. Three spe- 



