Velocity of Transmission of Disturbances through Sea-water. 497 



air-space at one end (p. 66), and in the case of dynamite (p. 82) in a 

 "tin case, with saw-dust tamping" (Appendix B, p. 433). The 

 sympathetic explosion of dynamite and guncotton had also been 

 investigated by General Abbott, with the general result (pp. 122 et seq.) 

 that as a distinct mode of explosion it does not exist. 



As this conclusion agrees entirely with the one to which we were 

 led, both with explosions by gnncotton in air and water, and explo- 

 sions of gnncotton, gelatine- dynamite, dynamite No. 1, and diazo- 

 benzene nitrate on one side of a large iron plate, the target charge 

 being on the other side, we did not pursue the matter further. We 

 may remark that we found diazobenzene nitrate a very good substance 

 to experiment on in this direction, as it is exceedingly sensitive, but 

 not so violent as silver fulminate. Like the latter and iodide of 

 nitrogen, we believe that its explosion can be caused by the friction 

 of the small crystals of which it is composed on one another. If two 

 heaps of this substance, placed on a thin iron plate, were protected 

 by cardboard cylinders without ends, resting on the plate supporting 

 the explosive and surrounding the latter, explosion always took place 

 at a greater distance when the supporting plate was sheet iron than 

 when it was a rather thicker pine board. Owing to the thinness of the 

 iron plate, the amplitude of the vibrations into which it was thrown 

 was greater than in the case of wood, and consequently the target 

 heap was more thrown about, and exploded (other things being equal) 

 at a greater distance. We have to thank Dr. Helms, Demonstrator 

 in Chemistry at the University, for his kindness in preparing the 

 diazobenzene nitrate for us ; it is both tiresome to make and delicate 

 to handle. 



On page 433 of his ' Submarine Mines and Explosives,' General 

 Abbott gives in an appendix an account of a remarkable explosion of 

 5 lb. of dynamite. In this experiment the axis of maximum effect 

 was bent out of the vertical (i.e., the normal to the water-surface 

 through the shot) to such an extent as to call for special comment. 

 A theory had been proposed by one of us which we thought might 

 account for this abnormal result, if it could be shown that it was 

 only an extreme case of a generally occurring phenomenon. With 

 the view of testing this theory, we decided that the best way would 

 be to find the velocity of transmission of explosive energy through 

 water, varying the quantity and nature of the explosive and its case, 

 and noting any irregularity that might occur. This, after two years' 

 work, we have succeeded in doing, extending our observations to gun- 

 cotton and Nobel's No. 1 dynamite, and varying the quantity of 

 explosive from 9 oz. up to 5 lb. charges. The distance over which the 

 velocity was measured was varied three times, from about 170, the 

 least, to 200 yards, the greatest distance. The results have been 

 such as to j ustify the title of this paper. 



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