This daring attack was no doubt the cause of Tilbury Fort being made to assume its present form. It is now a regular fortification, and may be justly looked upon as the key to the City of London. The plan of the building was laid out by Sir Martin Beckman, chief engineer to Charles II., who also designed the works at Sheerness. The foundation is laid upon piles driven down, two on end of each other, till they were assured they were below the channel of the river, and that the piles, which were pointed with iron, entered into the solid chalk rock. On the land side, the works are complete; the bastions are faced with brick. There is a double ditch, or moat, the innermost of which is 180 feet broad, with a good counterscarp, and a covered way marked out with ravelins and tenailles. There are some small brick redoubts; the chief strength, however, of this part of the fort consists in being able to lay the whole level under water, and, by that means, make it impossible for an enemy to carry on approaches that way. On the river side is a very strong curtain, with the picturesque water-gate shown in our engraving in the middle. Before this curtain is a platform, in the place of a counterscarp, on which are planted cannon of large size. These completely command the river, and would no doubt cripple the ships of an enemy attempting to pass in this direction. A few years ago there were placed on the platform 106 cannon, carrying from 24 to 46 pounds each, besides smaller ones planted between them. The bastions and curtains are also planted with guns. The circular tower shown in the engraving was in existence in the time of Queen Elizabeth, and was called the Block-house. RINGING THE CHANGES. It is curious to note the number of changes which may be rung on different peals. The changes on seven bells are 5,040; on twelve 479,001,600, which it would take ninety-one years to ring at the rate of two strokes in a second. The changes on fourteen bells could not be rung through at the same rate in less than 16,575 years: and upon four-and-twenty, they would require more than 117,000 billions of years. DISGRACEFUL STATE OF THE LONDON POLICE IN 1724.