496 Prof. R. Threlfall and Mr. J. F. Adair. On the 



" On the Velocity of Transmission through Sea-water of 

 Disturbances of large Amplitude caused by Explosions." 

 By Richard Threlfall, M.A., Professor of Physics, Uni- 

 versity of Sydney, and John Frederick Adair, M.A., 

 Demonstrator of Physics in the University of Sydney. 

 Communicated by Professor J. J. THOMSON, F.R.S. Re- 

 ceived March 14, 1889. Read March 21, 1889. 



[Plates 3, 4.] 



Part I. — Expebimental. 



During the latter months of the year 1886 and the first half of 

 the year 1887, experiments were undertaken by one of ns in conjunc- 

 tion with Lieutenant Ottley, R.N., of Her Majesty's ship " Nelson," 

 then stationed at Sydney, with the view of obtaining definite informa- 

 tion as to the existence or non-existence of the supposed phenomenon 

 of " explosion by influence." It had been previously discovered 

 (Threlfall, ' Phil. Mag.,' March, 1886) that in the case of small explo- 

 sions of fulminate of mercury under water, there was a sort of 

 directed effect due to want of symmetry in the disposition of obstacles 

 surrounding the centre of explosion. This suggested that a possible 

 explanation of the recorded cases of explosion by influence might be 

 found by a careful examination of the initial conditions. Since in 

 ordinary torpedo work in which the initial conditions of explosion 

 are greatly varied, cases of sympathetic explosion are generally 

 believed to have occurred, it was considered that the most hopeful 

 way of proceeding would be by endeavouring to obtain sympathetic 

 explosions between masses of explosive, fired under such conditions 

 as to preclude the possibility of directed action. To this end small 

 charges of guncotton were suspended in free air by strings, the 

 distance between the charges was measured, and one of them was 

 detonated. Out of about fifty experiments of this kind we did not 

 succeed in obtaining any explosion by influence, though the target 

 charge was generally blown to atoms. A similar series of experi- 

 ments, in which " 9-oz." disks of guncotton were wrapped in oil-silk 

 and exploded under water, resulted in the same conclusion. Explo- 

 sion of the target charge was only brought about when so close to 

 the exploding charge as to be exposed to explosive violence amply 

 sufficient to account for the explosion. In some cases the conditions 

 were varied by placing detonators in the target charge, but no excep- 

 tion to the general result was noticed. At this time we succeeded in 

 obtaining a copy of Major-General Abbott's ' Submarine Mines and 

 Explosives,' and there found that the directed action had been 

 noticed by him in the case of explosive mixtures in a case with an 



