The whistle showed the same intermittence as to period, but in an opposite sense; for when the whistle was faint the pipe was strong, and vice versa. To obtain the fundamental note of the pipe it had to be blown gently, and on the whole the whistle proved the most efficient in piercing the fog.
An extraordinary amount of sound filled the air during these experiments. The resonant roar of the Bayswater and Knightsbridge roads; the clangor of the great bell of Westminster; the railway-whistles, which were frequently blown, and the fog-signals exploded at the various metropolitan stations, were all heard with extraordinary intensity. This could by no means be reconciled with the statements so categorically made regarding the acoustic impenetrability of a London fog.
On the 11th of December, the fog being denser than before, I heard every blast of the whistle, and occasional blasts of the pipe, over the distance between the bridge and the eastern end of the Serpentine. On joining my assistant at the bridge, the loud concussion of a gun was heard by both of us. A police-inspector affirmed that it came from Woolwich, and that he had heard several shots about 2 p. m. and previously. The fact, if a fact, was of the highest importance; so I immediately telegraphed to Woolwich for information. Prof. Abel kindly furnished me with the following particulars:
"The firing took place at 1.40 p. m. The guns proved were of comparatively small size 64-pounders, with 10-lb. charges of powder.
"The concussion experienced at my house and office, about three-quarters of a mile from the butt, was decidedly more severe than that experienced when the heaviest guns are proved with charges of 110 to 120 lbs. of powder. There was a dense fog here at the time of firing."
These were the reports heard by the police-inspector; on subsequent inquiry it was ascertained that two guns were fired at about 3 p. m. These were the guns heard by myself.
Prof. Abel also communicated to me the following fact:
"Our workman's bell at the arsenal-gate, which is of moderate size and any thing but clear in tone, is pretty distinctly heard by Prof. Bloxam only when the wind is northeast. During the whole of last week the bell was heard with great distinctness, the wind being southwesterly (opposed to the sound). The distance of the bell from Bloxam's house is about three-quarters of a mile as the crow flies."
Assuredly no question of science ever stood so much in need of revision as this of the transmission of sound through the atmosphere. Slowly but surely we mastered the question; and the further we advanced the more plainly it appeared that our reputed knowledge regarding it was erroneous from beginning to end.
On the morning of the 12th the fog attained its maximum density. It was not possible to read at my window, which fronted the open
