AS A VEHICLE OF SOUND. 
213 
were unheard. The quiet of the park this evening, as contrasted with the resonant roar 
which filled the air on the two preceding days, was very remarkable. The sound, in 
fact, was stifled in the optically clear but acoustically more flocculent atmosphere. 
On the 13th, the fog being displaced by a thin haze, I went with my assistants again 
to the Serpentine. We could plainly see from one bank to the other, and far into Hyde 
Park beyond. When I rose this morning the vane pointed S.E., but before starting it 
had moved on to N.W., and on our return it pointed W. The motion of the air, how- 
ever, was of the lightest kind, at no time reaching a force of 1. The carriage-sounds 
were damped to an extraordinary degree. The roar of the Knightsbridge and Bayswater 
roads had subsided, the tread of troops which passed us a little way off was unheard, 
while at 11 a.m. both the chimes and the hour-bell of the Westminster clock were 
stifled. The air had become milder ; the hoar-frost had disappeared from the grass, 
though a residue still overspread the walks. At the end of the Serpentine I listened 
for the sounds from the bridge, and heard them. The pipe was in general the best, 
but all sounds were exceedingly faint, and the whistle was often inaudible. We 
reversed our positions, and I at the bridge listened for the sounds excited at the end of 
the Serpentine. With the utmost stretch of attention I could hear nothing. 
This failure of hearing occurred upon a day when the local noises were far less dis- 
turbing than they had previously been. The sounds of the carriage-wheels were low 
and muffled, the bells were for the most part inaudible, and, with the exception of one 
far faint sound, the locomotive-whistles were unheard. Subjectively considered all was 
favourable to auditory impressions ; but the very cause that damped the local noises 
extinguished our experimental sounds. The voice across the Serpentine to-day, with 
my assistant plainly visible in front of me, was distinctly feebler than it had been when 
each of us was hidden from the other in the densest fog. 
I sought to obtain a numerical estimate of the decay of the sound, and with this view 
stationed Mr. Cottrell at the eastern end of the Serpentine, while I walked along its 
edge from the bridge towards the end. The distance between these two points is about 
1000 paces. After I had stepped 500 of them the sound was not so distinct as it had 
been at the bridge on the day of densest fog : hence the optical cleansing of the air 
by the melting of the fog had so darkened it acoustically, that a sound generated at the 
end of the Serpentine was lowered to at most one fourth of its intensity at a point 
midway between the end and the bridge. 
I add two or three more of these domestic observations, and then pass to others made 
with actual fog-signals at the South Foreland. On several of the first days of this year 
I placed myself beside the railing of St. James’s Park, near Buckingham Palace, three 
quarters of a mile from the clock-tower. Not a single stroke of “ Big Ben” was heard 
at noon. These days were moist and warm, the air was calm, and the clock-tower in 
sight. On January 19 fog and drizzling rain obscured the tower; still from the same 
position I heard not only the strokes of the bell but also the preceding chimes of the 
quarter bells. The air was calm at the time. 
