1878.] Prof. Tyndall. Experiments on Fog-Signals. 255 



Tuddenham. St. Martin 10 miles Eeports very loud ; rolled away like thunder. 

 Christ Church Park .... 11 „ Eeport arrived a little more than a minute after 



flash. 



Nettlested Hall 6 „ Distinct in every part of observer's house. "Very 



loud in the open air. 



Bildestone 6 „ Explosion very loud, wind against sound. 



Nacton 14 „ Reports quite distinct — mistaken by inhabitants 



for claps of thunder. 



Aldboro 25 „ Eockets seen through a very hazy atmosphere ; 



a rumbling detonation heard. 

 Capel Mills 11 „ Eeports heard within and without the observer's 



house. Wind opposed to sound. 

 Lawford 15^ „ Eeports distinct : attributed to distant thunder. 



In the great majority of these cases, 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 a signal command- 

 ing 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 the Board of Trade actually proposed a light- and- sound 

 rocket as a signal of distress, which proposal was subsequently 

 realised, but in a form too elaborate and expensive for practical use. 

 The idea of the gun-cotton rocket with a view to signalling in fogs is, 

 I believe, wholly due to 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 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 the loss of the 

 "Vanguard" I ventured to urge upon an eminent naval officer the 

 desirability of having an organised 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 manipulated with ease and rapidity, while its 

 discharges may be so grouped and combined as to give a most im- 

 portant 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 desirable, a fog-signal station 

 might be extemporised without difficulty. 



I have referred more than once to the train of echoes which accom- 

 panied 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 



