Transparency and Opacity of the Atmosphere. 379 



proof that it continued to be high. From 10 to 10.30 a.m., while 

 waiting for the blasts of the syren at a distance of 3 miles from 

 the Foreland, the continued reports of what we supposed to be the 

 musketry of skirmishing parties on land were distinctly heard by 

 us all. We afterwards learned that the sounds arose from the 

 rifle-practice on Kingsdown beach, 5| miles away. On July 3, 

 which, optically considered, was a far more perfect day, the 18- 

 pounder howitzer and mortar failed to make themselves heard at 

 half this distance. The 18 th was mainly occupied in determining 

 the influence of pitch and pressure on the syren-sound. Taking 

 the fluctuations of the atmosphere into account, I am of opinion 

 that the syren, performing from 2000 to 2400 revolutions a second, 

 or, in other words, generating from 400 to 480 waves per second, 

 best meets the atmospheric conditions. We varied the pressure 

 from 40 to 80 lbs. on the square inch ; and though the intensity 

 did not appear to rise in proportion to the pressure, the higher 

 pressure yielded the hardest and most penetrating sound. 



The 20th was a rainy day with strong wind. Up to a distance 

 of d\ miles the syren continued to be heard through the sea- and 

 paddle-noises. In rough weather, indeed, when local noises inter- 

 fere, the syren-sound far transcends all other sounds. On various 

 occasions to-day it proved its mastery over both gun and horns. 

 On the 21st the wind was strong and the sea high. The horn- 

 sounds, with paddles going, were lost at 4 miles, while the syren 

 continued serviceable up to 6^ miles. The gun to-day was com- 

 pletely overmastered. Its puffs were seen at the Foreland ; but 

 its sound was unheard when the syren was distinctly heard. Heavy 

 rain failed to damp the power of the syren. The whistles were 

 also tried to-day, but were found far inferior to the syren. On 

 the 22nd it blew a gale, and the ' Galatea ' quitted us. We made 

 observations on land on the influence of the wind and of local noises. 

 The shelter of the Coastguard Station at Cornhill enabled us to hear 

 gun-sounds which were quite inaudible to an observer out of 

 shelter ; in the shelter also both horn and syren rose -distinctly in 

 power ; but they were also heard outside when the gun was quite 

 unheard. As usual, the sound to leeward was far more powerful 

 than those at equal distances to windward. The echoes from the 

 cloudless air were to-day very fine. On the 23rd, in the absence of 

 the steamer, the observations on the influence of the wind were 

 continued. The quenching of the gun-sounds in particular to wind- 

 ward was well illustrated. All the sounds, however, gun included, 

 were carried much further to leeward than to windward. The 

 effect of a violent thunderstorm and downpour of rain in exalting 

 the sound was noticed by observers both to windward and to lee- 

 ward of the Foreland. In the rear of the syren its range to-day 

 was about a mile. At right angles to the axis, and to windward, 

 it was about the same. To leeward it reached a distance of 7i| 

 miles. 



On the 24th, when observations were made afloat in the steam- 

 tug ' Palmerston,' the syren exhibited a clear mastery over gun and 



