$10 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 some 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 Eichard 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, hand! ness, 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 the 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 funda- 
* See also " Philosophical Transactions " for 1874, p. 183. 
