284 FRAGMENTS OF SCIENCE 



squalls of snow and hail, the direction of the sound being 

 at right angles to that of the wind. Five series of obser- 

 vations were made on board the "Vestal," at distances 

 varying from 3 to 6 miles. The mean value of the explo- 

 sions in the air exceeded that of the explosions near the 

 ground by a small but sensible quantity. At Windmill 

 Hill, Gravesend, however, which was nearly to leeward, 

 and 5% miles from the firing-point, in nineteen cases out 

 of twenty-four the disk fired near the ground was loud- 

 est; while in the remaining five the rocket had the 

 advantage. 



Toward the close of the day the atmosphere became 

 very serene. A few distant cumuli sailed near the hori- 

 zon, but the zenith and a vast angular space all round it 

 .were absolutely free from cloud. From the deck of the 

 "Galatea" a rocket was discharged, which reached a great 

 elevation, and exploded with a loud report. Following 

 this solid nucleus of sound was a continuous train of 

 echoes, which retreated to a continually greater distance, 

 dying gradually off into silence after seven seconds' dura- 

 tion. These echoes were of the same character as those 

 so frequently noticed at the South Foreland in 1872-73, 

 and called by me "aerial echoes." 



On the 23d of March the experiments were resumed, 

 the most noteworthy results of that day's observations 

 being that the sounds were heard at Tillingham, 10 miles 

 to the N.E.; at West Mersea, 15| miles to the N.B. by 

 B.; at Brightlingsea, 17K miles to the N.E.; and at Clac- 

 ton Wash, 20% miles to the N.E. by % E. The wind 

 was blowing at the time from the S.E. Some of these 

 sounds were produced by rockets, some by a 24-lb. how- 

 itzer, and some by an 8-inch Maroon. 



