The San Francisco Real Estáte Circular says: It ia asserted by competent engineers that the motive power used ou the Clay street hill railroad will, beyond a doubt, be used on all the street railroads of this and every other city of the United States within a few years. Tho Clay street hill road carries 3,000 passengers daily. Its cara are hauled up a grade which, in a distance of 2,800 feet, uiakes an ascent of 280 feet, or one iu thirteen. ïhe total length of the portion of the road on which tho endlesa stoel-cable ropo is used ig nearly 3,500 feet. ünly 1,700 lbs. (say three-quarters of a ton) of coal are used daily in furnishing the requisito motive power. If the road were extended to Van Ness avenue, it is asserted (we know not how truly) that one ton of coal por day would furnish all the steam roquisite to draw the cars both ways. Uuder these circuir) stances, it is as absurd and wasteful to continue to use üorses on street car lines as it would be to use them in raising ore out of the depths of the mines of the Comstock lodo. There is not one quarter the wear and tear on the cars when propelled by this system, and tho rails are not a projecting nuisanco to other vehicles, as in the case of the ordinary hoise car rails. The waste in power by the use of horses is as great as the iucreased expense. A inuch greater degree of speed than the snail-liko rate of the Clay street hill railroad can be attained with perfect safety and with littíe or no in crease of expense. On the steepest asceuding grade the car can be stopped in a distance of two and a half feet, and on the steepest descending grade in five feet. The time lost in stopping borse cari is ten per cent. The time is not fai distant when this mode of propelling street cars will )o m u-iH Bverywhere.