The practical question which has to be answered in every case where sewage is proposed to be discharged into a river requires to be approached from two points. The first is whether a nuisance will be caused at the spot to which objection would be taken. If this is likely to be the case, then the fact that the sewage will get purified in a short run of the river does not meet the objection. The second point requires a careful consideration of the condition of the river, both from an engineering as well as from a chemical and biological point of view. Decisions on these matters have too often been arrived at in a rough and ready way. They require skillful treatment, as the interests--both commercial and hygienic--which are affected are too great to permit of them being dealt with by any who are not well informed and careful. The general conclusions which we deduce from our observations are as follows: 1. That chemical precipitation is not so necessary now as it was considered to be a few years ago, in cases where land for irrigation is not procurable. 2. That the efforts to profitably remove the manurial elements from sewage by chemicals not having been successful, the system should be adopted _per se_ only where a filtration area cannot be obtained. 3. That the success which has attended the construction of filtration areas where the land is clayey, and the successful results which have been obtained from a combined straining of sewage and of subsequent filtration through small areas of artificial filters, point to the adoption of one or other of these systems in many cases where chemical treatment would previously have been advised. 4. That the injurious effects of passing untreated sewage into a river depend upon not merely the relative volumes of the sewage and the river, but chiefly upon the power of the river to oxidize the sewage, which power is in proportion to the extent of oxidation of the river itself. NEW YORK CITY STREET CARS. An article in the local news columns of the _Tribune_ says: