310 FRAGMENTS OF SCIENCE. 



In the great majority of these oases, the direction of the 

 sound enclosed a large angle with the direction of the wind. 

 In eome cases, indeed, the two directions were at right 

 angles to each other. It is needless to dwell for a moment 

 on the advantage of possessing a signal commanding ranges 

 such as these. 



The explosion of substances in the air, after having been 

 carried to a considerable elevation by rockets, is a familiar 

 performance. In 1873, moreover, the Board of Trade 

 proposed a light-and-sound rocket as a signal of distress, 

 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 signaling in fogs is, I believe, 

 wholly due to Sir Richard Collinson, the deputy master 

 of the Trinity House. Thanks to the skillful aid given by 

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

 Brock, that idea is now an accomplished fact; a signal 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 lightships, 

 but in the navy also it may be turned to important 

 account. Soon after tire loss of the Vanguard I ventured 

 to urge upon an eminent naval officer the desirability 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 coast, 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 Report on 

 Fog-signals, addressed to the Corporation of Trinity 

 House in 1874.* To these echoes I attached a fuuda- 



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



