AS A VEHICLE OF SOUND. 
193 
angles to the direction of the sound. This variance in the records on shore and 
afloat is not uncommon at the Foreland, the formation of the land giving rise to local 
currents of air. 
At a distance of 10 miles the horn once or twice yielded a plain sound, while the 
American whistle seemed to surpass the horn. We waited here for some time: at 10^ 
miles occasional blasts of the horn came to us, but after a time all sound ceased to be 
audible ; it seemed as if the air, after having been exceedingly transparent, had become 
gradually more opaque to the sound. 
Returning along the same line, we halted and listened at a distance of 8 ^ miles. The 
sounds were certainly much feebler than at 9 miles upon our journey out: it required 
attention and quiet on board to hear them at all. The haze continued, the cliffs of the 
Foreland being still hidden. At 6 miles we again halted : the sounds were indistinct, 
and not at all equal to those heard at 9|- miles in coming out ; they seemed, moreover, 
to have fallen in pitch : one of the observers described them as having degenerated to a 
kind of rumble. The sound as we approached the station became more and more 
unsatisfactory, and finally ceased. This we learned afterwards to be due to the breaking 
of the 2-inch reed of a wide horn. A narrower horn, which yielded a sound nearly 
equal to the large one, was used in the subsequent experiments. 
At 4.45 p.m. we spoke the ‘Triton,’ and took the master of the Varne light-ship on 
board the ‘ Irene.’ He and his company had heard the sound at intervals during the 
day, although he was dead to windward and distant 12f miles. All day long, however, 
the wind continued light, the force being only 2. 
Here a word of reflection on our observations may be fitly introduced. It is, as already 
shown, an opinion entertained in high quarters that the waves of sound are reflected at 
the limiting surfaces of the minute particles which constitute haze and fog, the alleged 
waste of sound in fog being thus explained. If, however, this were an efficient practical 
cause of the stoppage of sound, and if clear calm air be, as alleged, the best vehicle, it 
would be impossible to understand how to-day, in a thick haze, the sound reached a 
distance of 12f miles, while on May 20, in a calm and hazeless atmosphere, the maxi- 
mum range was only from 5 to 6 miles. Such facts foreshadow a revolution in our 
notions regarding the action of haze and fogs upon sound. 
Steaming directly in towards the Foreland, at 4| miles, with the paddles going, the 
sounds were well heard ; at 3§ miles upon the same bearing the loudest sound was 
very full. We steamed towards Dover Pier end, and at 2 -^q miles from the station, on 
the line between it and the pier, all sounds, as usual, fell considerably. At a distance 
of 1^ mile on the same line the loudest sound emitted by the horn during its rotation 
was very feeble. Inasmuch as this extraordinary subsidence of the sound occurred when 
the horn was turned towards us, it cannot be referred to the deviation from the axis : 
as already explained (§ 4), it is in part due to the weakening of the direct waves by 
diffraction, and in part, doubtless, to interference. 
Wishing to examine the condition of the sound at the other side of the Foreland, we 
mdccclxxiv. 2 c 
