14 SEPTEMBER 1850, Page 10

Mr. J. Walker, the eminent engineer, who has conducted the

repairs and alterations of Blackfriar's Bridge in progress for some years past, has reported on the danger popularly apprehended from the sinking of the pier. The depression, from the 26th of June to the 24th August, was one inch; and there has been no further depression to the 13th September. The depression was caused by the deepening of the channel six feet below the beads of the piles which enclose the foundation; and has been cured by refilling the bed of the channel with 3000 tons of stone materials.

The last tube in the Britannia Bridge was joined, yesterday, with the other tubes already in position, and lodged in its permanent resting-place. The structure as a bridge is now complete, and ready for inspection by the Government officer.

"Some of the acoustic effects produced by the bridge are interesting. The report of a pistol fired beneath the bridge is repeated three or four times. The rapid repetition of echoes from each of the T irons on the side of the tube gives rise to a shrill whirring musical note. When any violent noise is produced on the adjacent shore, the note is the same, whether produced by the blows of the riveters or the report of a cannon, and corresponds to the low D on a concert-flute. The cells of the top and bottom form excellent speaking-tubes, and oonversatien may be carried on through them even in a faint whisper. By elevating the voice, persons may converse through the entire length of the bridge, a distance of more than 600 yards. If one end of the cells be closed, they return a powerful echo ; but, although a whisper is thus distinctly repeated, the loudest whistle does not appear capable of re- turning any echo."

A charge of nearly twelve tons of gunpowder will be exploded in the Cliffs at Seaford on Thursday, by the Royal Engineers. "The sea, for some time past, has been encroaching on that part of the coast between Newhaven Pier and the Cliff-end at Seaford. Such an explosion as the one contemplated will, it is expected, throw out an immense fall of cliff into the sea, forming an enormous chalk groyne ; which, it is hoped, will prevent the beach from drifting Eastward, thus weakening the natural barrier of shingle which prevents the progress of the sea inland."