380 Royal Institution : — Prof. Tyndall on the Acoustic 



horns. The maximum range was 7| miles. The wind had changed 

 from W.S.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 every- 

 where through Dover, rising over the moaning of the wind and all 

 other noises. It was heard at a distance of 6 miles from the Pore- 

 land, on the road to Folkestone, and would probably have been heard 

 all the way to Polkestone 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 transpa- 

 rency, 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-J-, 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 Fore- 

 land at the greater distances being quite hidden ; still the gun- and 

 syren-sounds reached, on the bearing of the Yarne light-vessel, to a 

 distance of 1 1-J miles. The syren was heard through the paddle- 

 noises at 9| miles, while at 8-J- miles it became efficient as a signal 

 with the paddles going. The horns were heard at 6 j miles. This 

 was during calm. Subsequently, with a wind from the N.N.W., 

 no sounds were heard at 6A- miles. On land, the wind being across 

 the direction of the sound, the syren was heard only to a distance 

 of 3 miles N.E. of the Foreland ; in the other direction it was heard 

 plainly on Polkestone Pier, 8 miles distant. Both gun and horns 

 failed to reach Polkestone. 



Wind, rain, a rough sea, and great acoustic opacity character- 

 ized October 31. Both gun and horns were unheard 3 miles away, 

 the syren at the same time being clearly heard. It afterwards 

 forced its sound with great power through a violent rain-squall. 

 Wishing the same individual judgment to be brought to bear upon 

 the sounds on both sides of the Foreland, in the absence of 

 our steamer, which had quitted us for safety, I committed the ob- 

 servations to Mr. Douglass. He heard them at 2 miles on the 



