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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 assistant 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 Tyndall: 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 Edwards down to record the observations....

"Very truly yours,⁠Fred. Arrow."

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 Troughton (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 (12³⁄₄ 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.