Our readers are apprised that the poet Willis has for some time past, been employed in making the grand tour of Europe--a kind of literary reconnoissance, not only for his own benefit and gratification, but also for the purpose, we suppose, of enriching the columns of the New York Mirror (of which periodical he is one of the Editors,) with the various results of his observation. With many of his letters, or "first impressions" as they are called, we acknowledge ourselves to have been much delighted. His sketches of character and scenery are generally very impressive, and whilst on the one hand he avoids the too common fault of American writers,--a wearisome profusion of words--he does not, on the other, disdain the graces of ornament, or the beauties of amplification. It appears that he is at last peeping into the concerns of our venerable ancestor, John Bull. We hope that he will give a fair and candid account of the old gentleman's virtues, as well as his faults and peculiarities, "nothing extenuating, nor setting down aught in malice."--The following letter is very interesting. WILLIS'S IMPRESSIONS OF LONDON. From the top of Shooter's Hill we got our first view of London--an indistinct, architectural mass, extending all round to the horizon, and half enveloped in a dim and lurid smoke. "That is St. Paul's!--there is Westminster Abbey!--there is the Tower of London!" What directions were these to follow for the first time with the eye! From Blackheath, (seven or eight miles from the centre of London,) the beautiful hedges disappeared, and it was one continued mass of buildings. The houses were amazingly small, a kind of thing that would do for an object in an imitation perspective park, but the soul of neatness pervaded them. Trellises were nailed between the little windows, roses quite overshadowed the low doors, a painted fence enclosed the hand's breadth of grass-plot, and very, oh, _very_ sweet faces bent over lapfuls of work beneath the snowy and looped-up curtains. It was all home-like and amiable. There was an _affectionateness_ in the mere outside of every one of them. After crossing Waterloo bridge, it was busy work for the eyes. The brilliant shops, the dense crowds of people, the absorbed air of every passenger, the lovely women, the cries, the flying vehicles of every description, passing with the most dangerous speed--accustomed as I am to large cities, it quite made me giddy. We got into a "jarvey" at the coach-office, and in half an hour I was in comfortable quarters, with windows looking down St. James'-street, and the most interesting leaf of my life to turn over. "Great emotions interfere little with the mechanical operations of life," however, and I dressed and dined, though it was my first hour in London.