The German _Verein zur Bedförderung des Gewerbefleisses_ offers the following, among other prizes, for essays on technical subjects: One thousand marks _(£50)_ for a comparative examination of the various methods hitherto used for determination of the hardness of metals, with an exposition of their sources of error and limits of accuracy. It is stated, as a reason for offering the prize, that the methods for making the required tests are but yet little developed, and that no thorough comparison has yet been made of the various methods. The hardness of metals and alloys being a very important factor in several processes, a really good method of determination is highly desirable. Three thousand marks (£150) for the best essay on the resistance to pressure of iron work in buildings, at increased temperatures. It appears that after a certain fire in a manufactory at Berlin, the police authorities issued notices concerning the use of cast-iron columns in high buildings, and that these notices encountered great opposition in many quarters, as it was considered that neither practice nor theory had yet shown any proof that cast iron is less trustworthy than wrought iron in cases of fire. * * * * * A brilliant black varnish for iron, stone, or wood can be made by thoroughly incorporating ivory black with common shellac varnish. The mixture should be laid on very thin. But ordinary coal tar varnish will serve the same purpose in most cases quite as well, and it is not nearly so expensive. * * * * * STEAM YACHTS. Although the racing of steam yachts as a recognized sport has not made the progress that was at one time expected, yet the owner and crew of a crack vessel will take as much interest in her performance as those belonging to a sailing yacht, and hate to be passed quite as badly. In this way many informal matches come off, and some of these are for considerable distances. The _Field_ contains a notice of a run recently made from Plymouth Breakwater to Gibraltar, by the Juno, owned by Mr. Frank Millan, and the Queen of Palmyra, in which the former beat the latter by only five minutes. The time occupied was four days twenty hours, a fair, though not extraordinary, performance for vessels of this size. The Juno has always been considered a slow boat, but has been much improved lately by new machinery, which has been put in her by Messrs. Day, Summers & Co. Her best performance on the run was 235 knots in 21¾ hours. The Marchesa, Mr. C.T. Kettlewell, started from Plymouth on the 23d of last December, and made the run to Gibraltar in four days seventeen hours; while the Amy, starting on December 12, was four days thirteen hours from Cowes to Gibraltar. * * * * * A catalogue, containing brief notices of many important scientific papers heretofore published in the SUPPLEMENT, may be had gratis at this office.