TEANSHISSION OF SOUND BY THE ATMOSPHEEE. 
181 
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 windward, was well illustrated. All the sounds, how- 
ever, 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 leeward 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 7J miles. 
On the 24th, when observations were made afloat in the 
steam-tug Palmerston , the syren exhibited a clear mastery 
over gun and horns. The maximum range was 7f miles. The 
wind had changed from W.S.W. to S.E., then to E. As a 
consequence of this, the syren was heard loudly in the streets 
of Dover. On the 27th the wind was E.N.E. ; and the syren- 
sound penetrated everywhere through Dover, rising over the 
moaning of the wind and all other noises. It was heard at a 
distance of six miles from the Foreland on the road to Folke- 
stone, and would probably have been heard all the way 
to Folkestone had not the experiments ceased. Afloat and in 
the axis, with a high wind and sea, the syren, and it only, 
reached to a distance of six miles ; at five miles it was heard 
through the paddle noises. On the 28th further experiments 
were made on the influence of pitch , the syren when generating 
480 waves a second being found more effective than when 
generating 300 waves a second. The maximum range in the 
axis on this day was 7-J miles. 
The 29th of October was a day of extraordinary optical 
transparency, but by no means transparent acoustically. The 
gun was the greatest sufferer. At first it was barely heard at 5 
miles ; but afterwards it was tried at 5^, 4-J, and 2 J miles, and 
was heard at none of these distances. The syren at the 
same time was distinctly heard. The sun was shining 
strongly ; and to its augmenting power the enfeeblement of 
the gun-sound was doubtless due. At 3^ miles, subsequently, 
dead to windward, the syren was faintly heard ; the gun was 
unheard at 2| miles. On land the syren and horn-sounds were 
heard to windward at 2 to 2 J miles, to leeward at 7 miles ; 
while in the rear of the instruments they were heard at a 
distance of 5 miles, or five times as far as they had been heard 
on October 23. 
The 30th of October furnished another illustration of the 
fallacy of the notion which considers optical and acoustic 
transparency to go hand in hand. The day was very hazy, the 
white cliffs of the Foreland at the greater distances being 
