An interesting use of the sub-way telegraph may be here noticed. In proportion as the use of Greenwich time has become familiar on all the English railways, so has it become important to ascertain this time with precision, in such a way as to enable all the station-clocks to be regulated thereby. This is one purpose of the time-ball in the Strand. The Electric Telegraph Company, the South-Eastern Railway Com pany, and the Astronomer Royal, have acted in conjunction in the establishment of this plan. A subterranean wire has been carried from the Observatory, through Greenwich Park, and across Blackheath to the Lewisham station of the North Kent Railway ; thence to the London Bridge station ; and thence to the Telegraph office in the Strand. At the top of this office has been erected a hollow shaft, up the interior of which the electric wire is carried, and a large light bail, capable of moving eight or ten feet vertically, slides easily up and down near the top of the shaft. At ten minutes before one o'clock each day the ball is raised nearly to the top of its shaft or spindle ; and at five minutes before one it is raised quite to the top. At one o'clock precisely, exact to a single second, the great or master-clock at Greenwich Observatory puts in action a small piece of mechanism which sends an electric shock through the wire to the Strand ; the wire at this end is connected with another piece of mechanism, which releases the ball and allows it to fall suddenly. The ball falls upon a kind of piston in
an air-cylinder, so as to break the force of the concussion. As this ball is 130 feet above the level of the Thames ; as it is six feet in diameter, exhibits bright colours, and falls through a considerable space, its descent can be seen for a great distance on all sides ; and all who choose to regulate their clocks and watches by this standard can do so. An electric clock with four dials, illuminated at night, has been put up on a pillar in front of the office ; it indicates Greenwich time at all hours. The various railway stations receive their time from the Strand office, which is the medium of communication from the Greenwich Observatory. There can be little doubt that these arrange ments will contribute powerfully to the adoption of Greenwich time in church clocks and other public clocks. 'So useful is this considered to be, that a plan has been under consideration for erecting an electric time-ball on the summit of the South Foreland ; the descent of such a time-ball at one o'clock each day, could be witnessed by the captains of ships many miles out in the Channel, who could regulate their chronometers by this means, as the time-ball would show Greenwich time. It was also proposed that the electric current should fire off a gun at the same time and place, so that the sound might be heard if the descent of the ball could not be seen. This proposal has actually been adopted at Edinburgh and elsewhere.