206 
PROFESSOR TYNDALL ON THE ATMOSPHERE 
At 7 miles distance the syren was not strong and the horn was very feeble. 
At 3 p.m. the gun was fired, and it sent to us a very faint report, hardly equal to the' 
sound of the syren. A dense shower now enveloped the Foreland. 
The rain at length reached us ; but although it was falling heavily all the way between 
us and the Foreland the sound, instead of being deadened, rose perceptibly in power. 
Hail was now added to the rain, and the shower reached a tropical violence. The deck 
was thickly covered with hailstones, which here and there floated upon the rain-water, 
the latter not having time to escape. We stopped. In the midst of this furious squall 
both the horns and the syren were distinctly heard ; and as the shower lightened, thus 
lessening the local pattering, the sounds so rose in power that we heard them at a 
distance of 7^ miles distinctly louder than they had been heard through the rainless 
atmosphere at 5 miles. This observation is entirely opposed to prevalent notions, but 
it harmonizes perfectly with the explanation of our experience on the 3rd of July, 
according to which water in the state of vapour , and so mixed with air as to form non- 
homogeneous parcels, acts powerfully in wasting sound. Under the action of a strong 
sun, prior to the rain, the air had been in this flocculent condition, but the descent of 
the shower restored in part the homogeneity of the atmosphere and augmented its 
transmissive power. 
At 4 p.m. the rain had ceased and the sun shone clearly out : the air was calm afloat, 
but W., with a force of 2, ashore. At 9 miles distance the horn was heard feebly, the 
syren clearly, while the howitzer sent us a loud report. All the sounds were better at 
this distance than they had previously been at 5^ miles ; from which it follows that the 
intensity of the sound at 5^ miles must have been augmented at least threefold by the 
descent of the rain. 
The other instance to which I have to refer occurred on the 23rd of October. Our 
steamer had forsaken us for shelter, and I sought to turn the weather to account by 
making observations on the influence of the wind. Mr. Douglass, the chief Engineer of 
the Trinity House, was good enough to undertake the observations N.E. of the Foreland ; 
while Mr. Ayres, the Assistant Engineer, walked in the other direction. At 12.50 p.m. 
the wind blew a gale and broke into a thunderstorm with violent rain. Inside and 
outside the Cornhill Coastguard Station Mr. Ayres heard the sound of the syren 
distinctly through the storm, and after the rain had ceased all sounds were heard 
distinctly louder than before. Mr. Douglass had sent a fly before him to Kingsdown ; and 
the driver had been waiting for fifteen minutes before he arrived. During this time no 
sound had been heard, though 40 blasts had been blown ; nor had the coastguard man 
on duty, who had been accustomed to observe the sounds, heard any of them throughout 
the day. During the thunderstorm, and while the rain was actually falling with a 
violence which Mr. Douglass assures me was more like the descent of a water-spout than 
of ordinary rain, the sounds became audible and were heard by all. Prior to the thunder- 
storm the atmosphere, according to my explanation, was rendered acoustically flocculent 
by wreaths and streaks of mixed air and vapour. Through the precipitation of the 
