178 
POPULAK SCIENCE EEVIEW. 
seven P.M., the intensity of the sound was at least thirty-six 
times its intensity at two p.m. 
On October 8 the observations were resumed, a steam syren 
and a Canadian whistle of great power being added to the list 
of instruments. A boiler had its steam raised to a pressure of 
70 lbs. to the square inch; on opening a valve this steam would 
issue forcibly in a continuous stream, and the sole function of 
the syren was to convert this stream into a series of separate 
strong puffs. This was done by causing a disk with 12 radial 
slits to rotate behind a fixed disk with the same number of slits. 
When the slits coincided a puff escaped ; when they did not 
coincide the outflow of steam was interrupted. Each puff of 
steam at this high pressure generated a sonorous wave of great 
intensity ; the successive waves linking themselves together to 
a musical sound so intense as to be best described as a con- 
tinuous explosion. 
During the earlier part of October 8 the optical transparency 
of the air was very great ; its acoustic transparency, on the 
other hand, was very defective. Clouds blackened and broke 
into a rain and hail-shower of tropical violence. The sounds, 
instead of being deadened, were improved by this furious squall ; 
and, after it had lightened, thus lessening the local noises, the 
sounds were heard at a distance of 7^ miles distinctly louder 
than they had been heard through the preceding rainless atmo- 
sphere at a distance of 5 miles. At 5 miles distance, therefore, 
the intensity of the sound had been at least doubled by the rain 
— a result entirely opposed to all previous assertions, but an 
obvious consequence of the removal by condensation and preci- 
pitation of that vapour the mixture of which with the air had 
been proved so prejudicial to the sound. On this day a depen- 
dence was established between the pitch of a note and its 
penetrative power — the syren generating 480 waves, being slightly 
inferior to the horns, while generating 400 waves a second it 
was distinctly superior. The maximum range on October 8 was 
9 miles. On October 9 the transmissive power had diminished, 
the maximum range being miles. On both these days the 
syren proved to be superior to the horns, and on some occasions 
superior to the gun. 
On the 10th and 11th, a gale having caused our steamer to 
seek safety in the Downs, we made land-observations. The 
duration of the aerial echoes was for the syren and the gun 9 
seconds, for the horns 6 seconds. The duration varies from day 
to day. We sought to estimate the influence of the violent 
wind, and found that the sound of the gun failed to reach us in 
two cases at a distance of 550 yards to windward, the sound of 
the syren at the same time rising to a piercing intensity. To 
leeward the gun was heard at five times, and certainly might 
