The _Park_, extending behind the hospital—open free to the public until dusk—comprehends a considerable space of ground, nearly 200 acres, of great natural and artificial beauty. A pathway amidst lines of tall trees leads to a piece of rising-ground or mount, which, on holidays, generally exhibits a mirthful scene, in which ‘running down Greenwich hill’ plays a great part. On the summit is the _Royal Observatory_, founded by George III. for the promotion of astronomical science, and the scene of the labours of some men of distinguished ability. An astronomer-royal, supported by a parliamentary grant, constantly resides and pursues investigations in the Observatory. From this spot British geographers measure the longitude. The collection of instruments kept and used in this building is superb and costly; but the public are not admitted to see them. An electric _time-ball_ falls every day at one o’clock precisely; and an _electric clock_, a _standard barometer_, and _standard measures of length_, (of rigorous accuracy,) are placed for public use by the side of the entrance-gates. Limehouse to North Woolwich.—If a stranger be willing to lay aside the ideas of mere _pleasure_ spots, he will find much to look at and think about in the stretch of river margin here denoted. First comes the _Isle of Dogs_, joining Limehouse on the east. This strange horseshoe-shaped piece of ground is almost wholly below the level of the river, the inroads of which are only prevented by embankments. The northern neck of the peninsula (for it is not strictly an island) is occupied by the West India Docks; the middle portion is not much appropriated to any useful purpose, on account of the lowness of the site; the river edge is fringed with shipbuilding and factory establishments. The _Great Eastern_ was here built at Messrs. Scott Russell’s works. A new church has been built at _Cubitt Town_, the name now given to the eastern part of the Isle. Next below the Isle of Dogs are _Poplar_ and _Blackwall_, now forming one town—observable for the shipyard of Messrs. Green, the terminus of the Blackwall Railway, the East India Docks, and two or three river-side taverns where _whitebait dinners_ are much in fashion during the season. Then comes the spot, Bow Creek, at which the River Lea enters the Thames, so closely hemmed in by shipyards and engine-factories, that the Lea itself can barely be seen. The great shipyard of the Thames Company, late Messrs. Mare’s, is situated here. Next we come to the extensive and convenient _Victoria Docks_, occupying ground which was previously mere waste. Beyond the Docks are new centres of population gradually springing up, called _Silvertown_ and _North Woolwich_, with large factories and a railway station. Still farther east, near _Barking Creek_, there may be seen the vast outfall of the great system of drainage for the northern half of the metropolis.