The Observatory at the top of yonder hill was placed there for the benefit of pilots and sailors, in order to find out the motions of the moon and the places of the fixed stars. It has a most wonderful clock, which keeps exact time, and which sets the time for all the clocks in England. For this purpose other clocks are connected with this one by telegraph wires, which carry the time forward, and bring back an answer. The current of electricity leaving Greenwich takes the signal given by this clock, and then brings back an answer from the other clocks, saying how far they are wrong. A gentleman was being taken round by the Astronomer Royal, and as they were passing in front of a galvanic battery the great clock at Westminster was replying. It was sending word that it was going well, and was only the twentieth part of a second show. Twice a day it sent word how it was going.
Uncle Jonathan, Walks in and Around London, 1895 (3 ed.)
Victorian London - Publications - History - The Queen's London : a Pictorial and Descriptive Record of the Streets, Buildings, Parks and Scenery of the Great Metropolis, 1896 - Greenwich Observatory
It was during the reign of Charles II., in the year 1675, that the famous Greenwich Observatory was founded, chiefly with a view to determining the longitude of ships at sea. The Observatory, which is built of materials taken from the Tower of London and Tilbury Fort, is set on a hill 180 feet high in Greenwich Park. Here the standard time is decided daily, and all manner of astronomical calculations are made with the fine instruments with which the Observatory is fitted. On the outer walls are standard measures of length, and a clock, showing the correct time. Mr. \V. H. M. Christie is the Astronomer Royal, being the eighth holder of the office; and the annual cost of the institution is about £11,000.