64 Prof. J. Tyndall on the [Jan. 15, 



which were quite inaudible to an observer out of shelter ; in the shelter 

 also both horn and syren rose distinctly in power ; but they were also heard 

 outside when the gun was quite unheard. As usual the sound to lee- 

 ward was far more powerful than those at equal distances to windward. 

 The echoes from the cloudless air were to-day very fine. On the 23rd, 

 in the absence of the steamer, the observations on the influence of the 

 wind were continued. The quenching of the gun-sounds, in particular, to 

 windward was well illustrated. All the sounds, however, gun included, 

 were carried much further to leeward than to windward. The effect of a 

 violent thunderstorm and downpour of rain in exalting the sound was 

 noticed by observers both to windward and to leeward of the Foreland. 

 In the rear of the syren its range to-day was about a mile. At right 

 angles to the axis, and to windward, it was about the same. To lee- 

 ward it reached a distance of 7 5 miles. 



On the 24th, when observations were made afloat in the steam-tug 

 1 Palmerston,' the syren exhibited a clear mastery over gun and horns. 

 The maximum range was 7| miles. The wind had changed from W.8.W. 

 to S.E., then to E. As a consequence of this, the syren was heard loudly 

 in the streets of Dover. On the 27th the wind was E.N.E. ; and the 

 syren-sound penetrated everywhere through Dover, rising over the moan- 

 ing of the wind and all other noises. It was heard at a distance of 

 6 miles from the Foreland on the road to Folkestone, and would probably 

 have been heard all the way to Folkestone had not the experiments 

 ceased. Afloat and in the axis, with a high wind and sea, the syren, 

 and it only, reached to a distance of 6 miles ; at 5 miles it was heard 

 through the paddle noises. On the 28th further experiments were made 

 on the influence of pitch, the syren when generating 480 waves a 

 second being found more effective than when generating 300 waves a 

 second. The maximum range in the axis on this day was 7^ miles. 



The 29th of October was a day of extraordinary optical transparency 

 but by no means transparent acoustically. The gun was the greatest 

 sufferer. At first it was barely heard at 5 miles ; but afterwards it was 

 tried at 5|, 4|, and 2| miles, and was heard at none of these distances. 

 The syren at the same time was distinctly heard. The sun was shining 

 strongly ; and to its augmenting power the enfeeblement of the gun- 

 sound was doubtless due. At 3| miles, subsequently, dead to windward, 

 the syren was faintly heard ; the gun was unheard at 2| miles. On land 

 the syren and horn-sounds were heard to windward at 2 to 2| miles, to 

 leeward at 7 miles ; while in the rear of the instruments they were heard 

 at a distance of 5 miles, or five times as far as they had been heard 

 on October 23. 



The 30th of October furnished another illustration of the fallacy of 

 the notion which considers optical and acoustic transparency to go hand 

 in hand. The day was very hazy, the white cliffs of the Foreland at the 

 greater distances being quite hidden ; still the gun- and syren-sounds 



