AS A VEHICLE OF SOUND. 
209 
Acquainted with the foregoing facts regarding the passage of sound through cambric, 
flannel, baize, and felt, the reader will be prepared for the statement that the sound- 
waves pass without sensible impediments through heavy artificial showers of rain, hail, 
and snow. 
§ 12. Action of Fog* Observations in London. 
But the mariner’s greatest enemy, fog, is still to be dealt with ; and here for a long 
time the proper conditions of experiment were absent. Up to the end of November 
we had had frequent days of haze, sufficiently thick to obscure the white cliffs of the 
Foreland, but no real fog. Still those days furnished demonstrative evidence that the 
notions entertained regarding the reflection of sound by suspended particles were wrong. 
On many days of the thickest haze the sound had twice the range .that it attained in 
other days of perfect optical transparency. Such instances dissolved the association 
hitherto assumed between acoustic and optic transparency, but they left the action of 
dense fogs undetermined. 
I conferred with the Elder Brethren as to the possibility of transferring the instru- 
ments to some portion of the coast more favoured by fogs than the South Foreland ; but 
after due consideration the probability of spring fogs seemed so great, that it was decided 
to leave the instruments undisturbed and to await the expected appearance of the fog- 
Other duties called me to London, where on December 9th a memorable fog set in. I 
telegraphed to the Trinity House, suggesting some gun observations. A prompt reply 
informed me that such observations would be made in the afternoon at Blackwall or in 
its neighbourhood. I went to Greenwich in the hope of hearing the guns across the 
river ; but, owing to the delay caused by the fog, the firing had ended before I arrived. 
Over the river the fog was very dense, and through it came various sounds with great 
distinctness. The signal-bell of an unseen barge rang clearly out at intervals, and I 
could hear the hammering at Cubittstown, on the opposite side of the river. So distinct 
were the strokes that they appeared close at hand, though the works were upwards of 
half a mile away ; no deadening of the sound by the fog was apparent. 
Captain Atkins, assisted by Mr. Edwards, took charge of the gun-observations. Up 
to a distance of 2 miles the report was good ; at 2^- miles, with much land intervening, 
the report was still heard. The firing was from a 12-pounder carronade with a charge 
of 1 lb. of powder ; and this was heard through a dense fog distinctly better than the 
18-pounder with a 3-lb. charge, and an optically clear atmosphere, on the 3rd of July. 
The fog continuing unabated, on December 10 I sought to make some experiments 
upon a small scale over the Serpentine. I chose three organ-pipes of different lengths, 
a dog-whistle, a small bell struck by mechanism, and some percussion-caps. These were 
well heard across the Serpentine near the Watermen’s Boathouse. At the same time I 
could converse with ease with my assistant across the water. The bell, the percussion- 
caps, and the shortest organ-pipe proving least effective, in subsequent experiments they 
were discarded in favour of the others. 
In reply to my questions I was informed by two very intelligent policemen that they had 
MDCCCLXXIV. 2 E 
