OUR SUBMARINE DEFENCES. 
369 
a view to the probable action on the “ circuit-closers” of mines 
in the vicinity. 
A charge of 500 lbs. of gnn-cotton saturated with fresh water 
was placed in the service-pattern iron case, on the ground, at 
100 feet from the vessel’s side, where the depth of the sea was 
about eight fathoms (vide No. 1 in fig. 2). It was not 
expected that this first experiment would severely try the 
Oberon ; the intention of the programme was to begin at the 
greatest distance where an effect might be reasonably expected, 
and work gradually nearer and nearer. The progress of the 
successive experiments may be seen in fig. 2, where the situa- 
tion of each charge, with the date of the trial, is noted beneath 
it. The gun-cotton was used wet. This did not concern the 
object of this experiment, but incidentally it may be noticed 
that the effect of gun-cotton exploded wet is about the same as 
that of dry cotton. It was mentioned in the article on 
torpedoes referred to (Popular Science Review, April 1873), 
that gun-cotton could be exploded in a wet state, by means of a 
powerful detonator. The explanation appears to be that the 
vibration or wave of explosion generated by detonation differs 
so far from that of explosion by heat, that water is unable to 
absorb or take it up. Thus while heat has to overcome water 
by turning it into steam and expelling it at the loss of all the 
heat, specific and latent, required for such a process, the wave 
or explosion of detonation passes through it, unimpeded, just as 
completely as light passes through a glass window. 
We have given the details of the experiment of Aug. 6 at 
some length because they apply, with but little variation, to 
the entire series. The following summary may be given of the 
whole, which, with fig. 2, will furnish a full idea of the history 
of the attack. The charge employed in each case was 500 lbs. 
of gun-cotton, equal, as we have said, to 2,000 lbs. of powder. 
Trial No. 1, Aug. 6. — The mine was exploded at 100 feet, 
horizontally, from the starboard side of the vessel. It was at 
first thought that a considerable effect had been produced. 
The vessel leaked about the condensers, but it was found that 
the fault was only in imperfect fixing of the tubes. 
No. 2, Aug. 21. — The charge was exploded at 80 feet, hori- 
zontally ; produced insignificant effect. 
No. 3, Sept. 5. — At 60 feet, horizontally, the effect was again 
inconsiderable. 
No. 4, Sept. 26. — At 48 feet from the starboard side con- 
siderable effect was produced ; the condenser was broken, and 
other severe injuries were caused, so that it is very doubtful if 
the vessel could have continued her course. 
No. 5, Nov. 12. — To make use of the port side of the vessel 
the charge was brought over and floated at position shown in 
VOL. XIV. NO. LVII. B B 
