AS A VEHICLE OF SOUND. 
189 
In the experiments on the 19th and 20th of May, the superiority of the trumpets over 
the whistles was decided ; and indeed, with few exceptions, this superiority was main- 
tained throughout the inquiry. But there were exceptions. On June 2, for example, 
the sound of the whistles rose in several instances to full equality with, and on rare 
occasions subsequently even surpassed, that of the horns. The sounds were varied from 
day to day. On the date last mentioned a single horn was sounded, two were sounded, 
and three were sounded together ; but the utmost range of the loudest sound, even with 
the paddles stopped, did not exceed six miles. With the view of concentrating their 
power, the axes of the horns had been pointed in the same direction, and, unless stated 
to the contrary, this in all subsequent experiments was the case. 
On the 3rd of June the three guns already referred to were permanently mounted at 
the South Foreland. They were well served by gunners from Dover Castle. 
On June 3 dense clouds quite covered the firmament, some of them particularly black 
and threatening, but a marked advance was observed in the transmissive power of the 
air. At a distance of 6 miles the horn-sounds were not quite quenched by the paddle- 
noises ; at 8 miles the whistles were heard, and the horns better heard ; while at 9 miles, 
with the paddles stopped, the horn-sounds alone were fairly audible. During the day’s 
observations a remarkable and instructive phenomenon w r as observed. Over us rapidly 
passed a torrential shower of rain, which, according to Dekham, is a potent damper of 
sound. I could, however, notice no subsidence of intensity as the shower passed. It is 
even probable that, had my mind been free from bias, I should have noticed an aug- 
mentation of the sound, such as occurred with the greatest distinctness on various 
subsequent occasions during violent rain. 
The influence of “beats” was tried on June 3, by throwing the horns slightly out 
of unison ; but though the beats rendered the sound characteristic, they did not seem 
to augment the range. At a distance from the station curious fluctuations of intensity 
were noticed. Not only did the different blasts vary in strength, but sudden swellings 
and fallings off, even of the same blast, were observed. This was not due to any variation 
on the part of the instruments, but purely to the changes of the medium traversed by 
the sound. What these changes were shall be indicated subsequently. 
During the inquiry various shiftings of the horns and reeds were resorted to. with a 
view of bringing out their maximum power. The range of our best horns on June 10 
was 8f miles. The guns at this distance were very feeble. That the loudness of the 
sound depends on the shape of the gun was proved by the fact that thus far the howitzer, 
with a 3-lb. charge, proved more effective than the other guns. In the axis of the horns 
the sound manifests its greatest strength, falling sensibly off as the angular distance 
from the axis is augmented. Now the whistles have no such axes, but send their 
sound-waves with equal strength in all directions. Hence, as the horns pointed 
seaward, near the line joining the Foreland and the South Sand Head light-vessel on 
the one hand, and that joining the Foreland and the Admiralty Pier on the other, the 
whistles were sometimes more than a match for the horns. 
