192 
PROFESSOR TYNDALL ON THE ATMOSPHERE 
trumpet was pointed towards us to be represented by the number 10, the intensities 
when the trumpet was pointed in the other directions are represented by the other 
figures in the accompanying diagram*. 
These are the actual numbers set down during a series of 
observations, but they are not to be taken as representing 
any thing further than the general decadence of the sounds 
as the trumpet was more and more turned away from us. 
Indeed there is every reason to believe that the decay is 
sometimes more rapid and considerable than is indicated by 
these numbers. 
It may be remarked that a hoarding placed behind the 
trumpets contributed by reflection to augment the intensity of the sound when the 
trumpet was turned quite away from us. 
In the annexed sketch the judgment of an observer is expressed in words instead of 
numbers. It may be stated that at different periods of 
the same day, the opinion of the same observer varied 5 
as to the relative intensities of the sounds in the several 
positions of the horn. The observation here recorded 
For the better education of our ears we steamed 
closer to the Foreland, halting at 3-f- miles, and resting 
in this position during several rotations of the horn. 
The direct sound was very fine, the other sounds being 
expressed with approximate fairness by the numbers 
given in the first diagram. At 3-^ miles to windward 
(the wind, however, blowing only with a force of 2, and the water being smooth) the 
result was substantially the same. The day had become dark and lowering ; the black 
and threatening clouds formed a kind of ceiling overhead, thereby possibly aiding the 
sound f, while haze was diffused between us and the station. For the purpose of making 
a signal, we steamed within 2 miles of the Foreland. On steaming out again the sounds 
were heard for some time through the paddle-noises ; at about 4 miles distance they 
were lost, but they revived forcibly as soon as the paddles ceased moving ; on resuming 
the motion they continued to be heard up to a distance of 6f miles. 
At 7^ miles the paddles were eased, and a strong sound was heard ; at 9 A miles the 
sound was good, but it appeared to be of lower pitch than at a less distance. The haze 
at this time quite hid the Foreland, a somewhat staggering result considering the 
acoustic clearness of the atmosphere. The wind S.W., force 2, appeared to be dead 
against the sound ; but on shore it was N.W., with a force of 3, or nearly at right 
* To Capt. Drew, I believe, we were indebted for this idea of a dial. 
t This stands as it was written at the time ; but I believe it is still to be proved that clouds, as such, have 
any sensible power of reflection. 
