226 
PROFESSOR TYNDALL ON THE ATMOSPHERE 
ii was not heard. At 4.20 we halted; at the side of the combe nearest the signal-station. 
Here to me the report of the gun was fairly loud, but not loud to my companions. 
Wishing to ascertain how the sound fared to leeward, we followed the line of coast 
to St. Margaret’s Bay and reached the summit of the cliff above and a little beyond the 
coastguard station. Both the syren and the horn sent their sounds to us with extra- 
ordinary power. The gun fired at 4.50 was also very loud, though the distance far 
exceeded that at which the gun-shots had become entirely inaudible to windward. 
As we returned we heard several shots which were of a totally different character 
from those heard at the same distance to windward of the signal-station ; they were 
sharp and dense,, while the others resembled the shock of a soft body against sheet 
iron. 
On October 23 Mr. Douglass, at my request, was good enough to explore the atmo- 
sphere from the Foreland towards Deal, while Mr. Ayres undertook the observations on 
the Dover side of the Foreland. The wind, with a force of 6 to 8, blew from the W. and 
W.S.W. The instruments in use were the syren, the two upper horns, and the howitzer. 
They were all pointed southwards. 
In the case of Mr. Ayres, at 600 paces from the station the syren was heard distinctly, 
the horns indistinctly and only occasionally ; the gun was unheard. Between this point 
and another, 440 paces west of the Coastguard Station, or about 1^ mile west of the 
instruments, eight observations were made at different points. In three cases only was 
the gun heard ; in three only were- the horns heard occasionally and faintly ; in all 
cases the syren was heard. Against the wind the superiority of the syren over the horns, 
and more especially over the gun, is incontestable. 
At Bingwold, on the other side of the Foreland, distant 3 miles, and at Walmer, 
distant 3| miles, the gun yielded a loud report; the syren and horns also yielded a 
good sound. Near Deal barracks, 4^ miles, near the railway station, 5 miles, and near 
Sholden church, miles, the gun yielded a fair report : the syren was heard, being 
about equal to the gun. At 6 miles distance the gun was heard, but very feebly ; at 
6f miles and at 7^ miles neither gun nor horn was heard, while in both cases the syren 
was audible. On the Sandwich side of the Foreland, therefore, the sounds on this day 
were heard at least four times as far as on the Dover side, while in both directions the 
syren was furthest heard. 
On the 24th the wind shifted to E.S.E., and the sounds, which when the wind was 
W.S.W. failed to reach Dover, were now heard in the streets through thick rain. On 
the 27th the wind was E.N.E. In our writing-room in the Lord Warden Hotel, in the 
bedrooms, and on the staircase the sound of the syren reached us with surprising power, 
piercing through the whistling and moaning of the wind; which blew through Dover 
towards Folkestone. The sounds were heard at 6 miles from the Foreland on the Folke- 
stone road ; and had the instruments not then ceased sounding they might have been 
heard much further. At the South Sand Head light-vessel, on the opposite side, no sound 
had been heard throughout the day. On the 28th, the wind being N. by E., the sounds 
