Greenwich Park, that was first roughly enclosed by Duke Humphrey of Gloucester and his wife Eleanor in 1433, was further protected some two centuries later by a brick wall erected by order of James I. The grounds were laid out by the famous landscape gardener, Le Nôtre, chosen by Charles II., who took a great interest in the progress of the work, himself planting many trees, including the noble avenue of Spanish chestnuts that is still one of the most noteworthy features of the park. {113} It was the same monarch who decided to transform into an Observatory the tower built by Duke Humphrey, which had been the home for many years of the younger members of the royal family, and in which the Princess Mary, one of the daughters of Edward IV., died in 1482. Later the building, to which the inappropriate name of Mirefleur was given, was used as a prison, and in it Queen Elizabeth had the Earl of Leicester shut up after his marriage to the widowed Duchess of Essex. James I. gave the property to Henry Howard, Earl of Northampton, founder of the still flourishing Trinity Hospital, and he greatly enlarged the Tower, converting it into a really fine mansion. The work of transforming it into an observatory was entrusted to Sir Christopher Wren, who found it necessary to have the greater part taken down, but he used the old materials; and in spite of the many additions that have been made since his time, the group of buildings, with their numerous turrets and domes, harmonise well with each other and their surroundings. Through Greenwich Observatory runs the meridian line from which longitude is reckoned, and from it the exact time is conveyed by electricity every day at one o'clock to the chief towns of Great Britain. In it elaborate records are made of the daily changes in temperature, the direction of the wind, and many other data of importance to astronomical and meteorological science. The great telescope, that is twenty-eight feet long and has an object glass of twenty-eight inches, is the most powerful anywhere in use, and near to the chief entrance is the huge astronomical clock that shows the {114} true official time. Many distinguished men have held the important post of Astronomer-Royal at Greenwich, including Flamsteed, Halley, Bradley, and Sir George Airey, under whose enlightened auspices the observatory has won first rank amongst similar institutions elsewhere, a position it seems likely long to maintain if its interests are protected from the dangers that have recently begun to threaten them. The annual reports issued by the Astronomer-Royal are practically a history of astronomical science, and it is impossible to overestimate the value of the quiet, systematic, unremitting work done under his auspices all the year round, or of the unceasing vigilance of the experts whose business it is to make sure that all the instruments used are in the highest possible state of efficiency.