takes place, the conflict not anticipated in the early years of its application, but in the course of years becoming palpable. It is no other than the ordnance versus iron-plate warfare; if the one increases in force and magnitude, so the other must be fortified in ratio. Thus, if ships have to be protected from their assailants, so must the rivers, estates, parks, seats, and castles be protected from the other. Hence Corporations, in initiating sanitary improvements for themselves, are not justified, as hitherto, in neglecting the interests outside of their precincts; and, as justly observed by the Glasgow Deputation, those cities having a natural outlet apart from all other interests, are fortunate. This latter condition is oftener the case with seabound towns than with inland ones. Certain it is that the idea so often prevailing amongst sanitary engineers that their works are for ever, and all time to come, must be abandoned, and their judgment must be exercised, not as now to create works of magnitude far beyond present wants, but to institute systems to which least objections can be taken ultimately, or for the time being. The wants of the present population must not only be estimated, and of the future, but their capacity to bear the burden of taxation, hence, though working to an end, and on just principles, the consideration should be as to what was actually necessary, and no more, leaving their successors to continue the same. Without being attentive to these facts, the city populations may pay too dearly for the luxury of improvements or quasi improvements, and property may be overburdened by works which could perfectly well be held over. As an example of the conflict between interests, that takes place consequent on the modern introduction of town cleansing by water-gravitation, we turn to the greatest city in the world, where it has perforce had largest development. The outfall of the sewage, till recent years, was into the Thames, within the precincts of the city. This created nuisances which it was found desirable to remove; hence those measures were taken which have already been described in the preceding part of this paper. But, besides the Metropolitan Board of Works, there exists a Board of Conservators of the River Thames, having other interests than the population of London to take care of, and on which the operations of the former Board were felt to act detrimentally. In consequence of this, Captain Calver, R.N., F.R.S., was, by the secretary, directed to investigate and report on the subject* Thames Commission, 6th June, 1877. That gentleman acknowledged the receipt of the instructions, to wit; that he should direct his attention to some recent surveys which had been made by the officers of the Board, of that section of the River Thames extending from Woolwich to Erith, as well as to analytical examinations by