272 FKAGMENTS OF SCIENCE. 



2-oz. rocket. The former was recorded as 6 '9 and the 

 latter as 5*9, the value of the 4-oz. rocket being inter- 

 mediate between them. These results were recorded by 

 a number of very practised observers on board the 

 'Gralatea.' They were completely borne out 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-pounder gun fell far behind all the rockets, a 

 result, possibly, to be in part ascribed to the imperfec- 

 tion of the powder. The performance of the syren was, 

 on the whole, less satisfactory than that of the rocket. 

 The instrument was worked, not by steam of 70 Ibs. 

 pressure, as at the South Foreland, but by compressed 

 air, beginning with 40 Ibs. and ending with 30 Ibs. 

 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 be- 

 tween 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, however, 

 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 Ibs. was employed 

 to sound the syren, the rockets proved greatly superior 





