290 FRAGMENTS OF SCIENCE 



tress, which proposal was subsequently realized, but in a 

 form too elaborate and expensive for practical use. The 

 idea of a gun-cotton rocket fit for signalling in fogs is, I 

 believe, wholly due to Sir Kichard Collinson, the Deputy 

 Master of the Trinity House. Thanks to the skilful aid 

 given by the authorities of Woolwich, by Mr. Prentice and 

 Mr. Brock, that idea is now an accomplished fact ; a sig- 

 nal of great power, handiness and economy being thus 

 placed at the service of our mariners. Not only may the 

 rocket be applied in association with lighthouses and light- 

 ships, but in the Navy also it may be turned to important 

 account. Soon after the loss of the ** Vanguard" I vent- 

 ured to urge upon an eminent naval officer the desirabil- 

 ity of having an organized code of fog-signals for the 

 fleet. He shook his head doubtingly, and referred to the 

 difficulty of finding room for signal guns. The gun-cotton 

 rocket completely surmounts this difficulty. It is manip- 

 ulated with ease and rapidity, while its discharges may be 

 so grouped and combined as to give a most important 

 extension to the voice of the admiral in command. It is 

 needless to add that at any point upon our coasts, or upon 

 any other coast, where its establishment might be desir- 

 able, a fog-signal station might be extemporized without 

 difficulty. 



I have referred more than once to the train of echoes 

 which accompanied the explosion of gun-cotton in free air, 

 speaking of them as similar in all respects to those which 

 were described for the first time in my Eeport on Fog- 

 signals, addressed to the Corporation of Trinity House in 

 1874. ' To these echoes I attached a fundamental signifi- 



1 See also "Philosophical Transactions" for 1874, p. 183. 



