The cleansing of the streets and the removal of the impurities from the habitations appears to have been the subject of considerable attention at Paris of late years. An individual proposed to the administration of that city a mode of cleansing the streets and pavement, by sweeping all the refuse into the sewers which are discharged into the Seine, that had hitherto been daily gathered into heaps and carted away beyond the precincts. The minister of police thought it advisable to take the opinion of the Institute on the proposal. The superiority of the proposed mode of street cleansing was admitted, but the members of the Institute, to whom the subject was referred, having ascertained the quantity of rubbish which was daily collected in Paris, and also the quantity of water which flowed in the Seine during the summer-time, they found that this volume of water was 9600 times greater than the greatest quantity of filth and rubbish collected in the same length of time from the streets of Paris; and they reported as their conclusion, “that the quantity of dirt which would be thrown into the Seine, compared with the volume of water in the river, would be found to be so extremely small as to be absolutely inappreciable; that it was not from the consideration therefore of insalubrity that the project for cleaning the streets as proposed should be negatived, but solely because by that means there would be lost a quantity of most valuable manure, which was quite indispensable to the agriculture around Paris, and consequently to Paris itself.”[9] Mr. Roe has furnished me with a calculation made from the flow of water in the Thames, at a neap tide: taking the ebb, and comparing it with the quantity of deposit in the water running from the sewers from the whole of the metropolis (assuming that the sewerage bears the same proportion as the Holborn and Finsbury division), that the proportion of impurities to the volume of water of the Thames is as 1 to 10,100. If the surface cleansing of the streets were added to the ordinary mass of impurity, he calculates that the proportion held in suspension would then be about 1 to 5069. To this must be added the impurities from land-floods, and those from vessels in the river. The amount of impurity discharged from the sewers was calculated from the amount of deposit known to have been formed in several of them. The amount of impurity in the Thames would therefore be, at the least, double the amount of that calculated for the Seine.[10]