254 Prof. Tyndall. Experiments on Fog- Signals. [Mar. 21, 



of very practised observers on board the " Galatea." They were com- 

 pletely borne ont by the observations of the Coastguard, who marked 

 the value of the 8-oz. rocket 6'1, and that of the 2-oz. rocket 5"2. 

 The 18-ponnder gun fell far behind all the rockets, a result pro- 

 bably to be in part ascribed to the imperfection of the powder. 

 The performance of the syren was, on the whole, less satisfactory 

 than that of the rockets. The instrument was worked, not by steam of 

 70 lbs. pressure, as at the South Foreland, but by compressed air, 

 •beginning with 40 lbs. and ending with 30 lbs. pressure. The trumpet 

 was pointed to windward, and in the axis of the instrument the sound 

 was about as effective as that of the 8-oz. rocket. But in a direction 

 at right angles to the axis, and still more in the rear of this direction, 

 the syren fell very sensibly behind even the 2-oz. rocket. 



These are the principal comparative trials made between the gun- 

 cotton rocket and other fog-signals ; but they are not the only ones. 

 On the 2nd of August, 1877, for example, experiments were made at 

 Lundy Island with the following results. At 2 miles distant from the 

 firing point, with land intervening, the 18-pounder, firing a 3-lb. charge, 

 was quite unheard. Both the 4-oz. rocket and the 8-oz. rocket, how- 

 ever, reached an elevation which commanded the acoustic shadow, and 

 yielded loud reports. When both were in view, the rockets were still 

 superior to the gun. On the 6th of August, at St. Ann's, the 4-oz. and 

 8-oz. rockets proved superior to the syren. On the Shambles Light- 

 vessel, when a pressure of 13 lbs. was employed to sound the syren, the 

 rockets proved greatly superior to that instrument. Proceeding along 

 the sea margin at Flamboro' Head, Mr. Edwards states that at a dis- 

 tance of 1\ mile, with the 18-pounder gun hidden behind the cliffs, its 

 report was quite unheard, while the 4-oz. rocket, rising to an eleva- 

 tion which brought it clearly into view, yielded a powerful sound in 

 the face of an opposing wind. 



On the evening of February 9th, 1877, a remarkable series of 

 experiments was made by Mr. Prentice, at Stowmarket, with the 

 gun-cotton rocket. From the report with which he has kindly fur- 

 nished me I extract the following particulars. The first column in the 

 annexed statement contains the name of the place of observation, the 

 second its distance from the firing-point, and the third the result 

 observed : — 



Stoke Hill, Ipswich. ... 10 miles Rockets clearly seen and sounds distinctly heard 



53 seconds after the flash. 

 Melton 15 „ Signals distinctly heard. Thought at first that 



sounds were reverberated from the sea. 

 Franilinghani 18 ,, Signals very distinctly heard, both in the open 



air and in a closed room. Wind in favour of 



sound. 



Stratford. St. Andrews 19 „ Reports loud ; startled pheasants in a cover 



close by. 



