694 THE POPULAR SCIENCE MONTHLY. 



was heard striking loudly eleven. Toward evening this fog began to 

 melt away, and at six o'clock I went to the end of the Serpentine to 

 observe the effect of the optical clearing upon the sound. Not one of 

 the strokes reached me. At nine o'clock and at ten o'clock my assist- 

 ant was in the same position, and on both occasions he failed to hear 

 a single stroke of the bell. It was a case precisely similar to that of 

 December 13th, when the dissolution of the fog was accompanied by 

 a decided acoustic thickening of the air. 1 



Observations at the South Foreland. Satisfactory and indeed 

 conclusive as these results seemed, I desired exceedingly to confirm 

 them by experiments with the instruments actually employed at the 

 South Foreland. On the 10th of February I had the gratification of 

 receiving the following note and inclosure from the deputy-master 

 of Trinity House : 



"My dear Tyndaix: The inclosed will show how accurately your views 

 have been verified, and I send them on at once without waiting for the details. 

 I think you will be glad to have them, and as soon as I get the report it shall be 

 sent to you. I made up my mind ten days ago that there would be a chance in 

 the light foggy-disposed weather at home, and therefore sent the Argus off at 

 an hour's notice, and requested the Fog Committee to keep one member on 

 board. On Friday I was so satisfied that the fog would occur that I sent Ed- 

 wards down to record the observations. . . . 



" Very truly yours, Feed. Aeeow." 



The inclosure referred to was notes from Captain Atkins and Mr. 

 Edwards. Captain Atkins writes thus : 



"As arranged, I came down here by the mail express, meeting Mr. Edwards 

 at Cannon Street. We put up at the Dover Castle, and next morning at seven I 

 was awoke by the sounds of the siren. On jumping up I discovered that the 

 long-looked-for fog had arrived, and that the Argus had left her moorings. 



" However, had I been on board, the instructions I left with Trougbton (the 

 master of the Argus) could not have been better carried out. About noon the 

 fog cleared up and the Argus returned to her moorings, when I learned that 

 they had taken both siren and horn sounds to a distance of 11 miles from the 

 station, where they dropped a buoy. This I know to be correct, as I have this 

 morning recovered the buoy, and the distances both in and out agree with 

 Troughton's statement. I have also been to the Varne light-ship (12J miles 

 from the Foreland), and ascertained that during the fog of Saturday forenoon 

 they ' distinctly ' heard the sounds." 



Mr. Edwards, who was constantly at my side during our summer 

 and autumn observations, and who is thoroughly competent to form a 

 comparative estimate of the strength of the sounds, states that the 

 sounds were " extraordinarily loud," both Captain Atkins and himself 



1 A friend informs me that he has followed a pack of hounds on a clear, calm day 

 without hearing a single yelp from the dogs ; while on calm, foggy days from the same 

 distance the musical roar of the pack was loudly audible. 



