290 REPORT — 1851. 



Half a division of the small dial can be distinctly read ; hence we could 



observe an interval as small as ^L^5^^Ml=o"-006956, or less than, To'oodtbs 



2 



of one second. 



The general arrangement at first contemplated was as follows : — 



^ 



^. 



^ C2 Diag.9. 



s 



The range of half a mile extending from A to B, the powder was buried 

 at P, one extreme ; at the other was placed the seismoscope S and a chrono- 

 graph C^, so arranged, (see detail plate of apparatus) that on my releasing 

 it, contact was made right through the whole line of both wires v" and w 

 through the firing batteries at B, and through a magnetic coil attached to the 

 second chronograph at C (Sharp's), and so arranged that it released this 

 chronograph at the moment contact was made by me : the wires, each of 3 

 twisted galvanized iron wires severally of No. 13 wire-gauge, were soldered 

 together, and at first lying upon the sand, but afterwards insulated on wood- 

 stakes. According to this arrangement, when contact was made at C^ both 

 chronographs were released at once. The moment the explosion took place, 

 an assistant (William Mallet) stopped the chronograph C, placed within 150 

 yards or so of the charge ; and as soon as the wave reached me and was 

 seen in the seismoscope S, 1 stopped the second chronograph C'^ ; the first 

 chronograph C- showed the time of hang-fire, and the difference of these 

 chronographs the gross time of wave transit. 



On the 25th of October 1 84.9 this scheme was tried, the battery power being 

 12 cells of Bergin's battery, the surface in action of each plate being already 

 given. The cast iron in NOs-HSOg-^- HO, opposed to two zincs inSOg-f HO; 

 but it was found quite impossible either to release the chronograph C, or to 

 fire the powder at this range. It could not be done even when both wires 

 were completely insulated on wood stakes 4 or 5 feet high, driven into the 

 sand ; the battery wanted intensity. 



On consideration, it was determined wholly to alter this arrangement and 

 to fire from within a very short distance of the charge, and having two 

 batteries at this point, one (Bergin's) to fire the powder, and another (one of 

 Smee's with a large series of plates) to release by a magnetic coil the chro- 

 nograph at the seismoscope end at the moment that contact was made simul- 

 taneously through both batteries and the whole range of insulated wire, the 

 apparatus being such as to release the chronograph at the batteries to show 

 the hang fire also. 



Bergin's battery, as before, was used with 12 cells in action, the acids used 

 being for the cast iron porous cells equal volumes of commercial nitrous acid 

 and of commercial sulphuric acid and of water; and for the cells containing 

 the zinc, one volume of sulphuric acid of commerce and eight volumes of 

 water. Smee's battery consisted of 7 troughs in action, of silver and double 

 zincs, 6 series in each, each plate having an acting surface (one side) of 2^ 

 inches wide x 3^ inches deep, or in all a series of 42 pair of plates acting in 

 SOg-i-HO, diluted in the ratio of 1 volume of acid to 20 volum.es of water. 



On preliminary trials with priming cartridges only, this entire arrangement 

 was found to act perfectly in all respects, firing the powder and releasing the 

 chronographs with ease and certainty. 



The following code of signals was fixed upon, as the length of the range 



