The frequent and sudden changes of temperature in the last few weeks have made an extraordinary difference in the aspects of London street-traffic from day to day. We lately gave an illustration of the effects of a hard frost; our present subject is a companion picture to that Engraving; it shows the state of things occasioned by a thaw. The discomfort of walking in such mud as melted snow leaves upon our much-trodden thoroughfares is far worse than the danger of sliding when the pavement is glazed with ice. London mud is always disagreeable; and we believe there is no city in Europe where so little care is taken to abate this nuisance, or where the convenience of foot-passengers is so entirely disregarded by the legal custodians of the public highways. To go no further than the large provincial towns of England—it would not be endured; for instance, in Manchester that any of the streets should be left for twelve hours in so foul a condition as that of the Strand during many days of the last fortnight; when it might have been cleansed without difficulty, either by sweepers employed at night, or by the use of Whitworth’s machine—a mud-cart furnished with a revolving brush and scraper behind, which travels along the road, causing no interruption to the daily traffic. In this department, it must be confessed, the municipal administration of London is greatly at fault; and it would be instructive to reckon the enormous cost of its neglect in the matter of street mud. Such a calculation would include—first, the cost of boots and shoes, of stockings, trousers, and crinolines, sacrificed by the unhappy pedestrians who venture abroad at this season; secondly, the loss of health, and sometimes of life, from the catarrhs, coughs, and rheumatisms which wet feet are apt to engender; thirdly, the damage to horses and carriages; and, lastly, the waste of an immense quantity of material which should be almost as valuable as the sewage itself for the purpose of agricultural manure. In addition to these ills, we have reason to believe that the mischief done by neglected street mud to the sanitary condition of London extends also to those who never walk out in bad weather, for it keeps up a general dampness of the atmosphere, attracts and retains the fogs, and, after the dry winds of March or the heat of sunny days shall have caused the last vestige of mud to disappear, it will then be converted into dust, which, as it contains minute particles of stone from the roads, mixed with the noxious atoms of decomposed animal matter, is a most unwholesome compound to be inhaled by the throats of men and women. Thus much we have felt it our duty to say of the remoter and more general injuries occasioned by the utter lock of provision for the removal of the metropolitan mud. The miseries depicted on our next page are indeed the immediate consequence of a visitation of nature which is a common incident; of this season in a climate so uncertain as ours; but these miseries would very soon be abated if we bad a proper system of cleansing the streets. The poor mendicant sweeper at the crossing should be relieved of an office which ought to be more efficiently performed by an apparatus under the direction of the Metropolitan Board of Works.