In the annals of the world there have never been such rapid changes and such vast improvements as have occurred in this metropolis during the last seven years. We have no occasion now to refer to Pennant to produce exclamations of surprise at the wonderful changes in London; our own recollections are sufficient. Oxford-street seems half a mile nearer to Charing Cross than in the days of our youth. Swallow-street, with all the dirty courts in its vicinity, have been swallowed up, and replaced by one of the most magnificent streets in Europe; a street, which may vie with the Calle d’Alcala in Madrid, with the Quartier du Chapeau Rouge at Bourdeaux, or the Place de Louis Quinze at Paris. We must, for the present, overlook the defects of the architectural detail of this street, in the contemplation of the great and general improvement which its construction has produced in the metropolis. Other streets are proposed by the same active genius under which Regent-street has been accomplished; the vile houses which surrounded and hid the finest portico in London--that of St. Martin’s church--are already taken down; a square is to be formed round this building, with two large openings into the Strand, and plans are already in agitation to lay open other churches in the same manner. Even the economical citizens have given us a peep at St. Bride’s--being ashamed again to hide beauties which accident had given them an opportunity of displaying to greater advantage. One street is projected from Charing Cross to the British Museum, terminating in a square, of which the church in Hart-street is to form the centre; another is intended to lead to the same point from Waterloo-bridge, by which this structure, which is at present almost useless, will become the great connecting thoroughfare between the north and south sides of the Thames: this street is, indeed, a desideratum to the proprietors of the bridge, as well as to the public at large. Carlton-house is already being taken down--by which means Regent-street will terminate at the south end, with a view of St. James’s Park, in the same manner as it does at the north end, by an opening into the Regent’s Park. Such is the general outline of the late and the projected improvements in the heart of the metropolis; but they have not stopped here. The king has been decorating Hyde Park with lodges, designed by Mr. Decimus Burton, which are really gems in architecture, and stand unrivalled for proportion, chasteness, and simplicity, amidst the architectural productions of the age. Squares are already covering the extensive property of lord Grosvenor in the fields of Chelsea and Pimlico; and crescents and colonnades are planned, by the architect to the bishop of London, on the ground belonging to the diocese at Bayswater.