No ship has been built to stand the shock of a 3,500 pound bolt moving at the velocity of 1,300 or 1,500 feet a second. EAR TRUMPETS FOR PILOTS. Prof. Henry has turned his attention to the discovery of means for increasing the distinctness of sound signals at sea. It is a very large hearing trumpet, projecting mouth foremost from the top of the pilot-house of a steamboat. But he soon found that a single hearing trumpet would not answer the purpose, for though it greatly augmented the perceptive power of the ear, it destroyed the capacity of that organ for distinguishing the direction of sound. For this purpose two ears are necessary. Prof. Henry then made use of two hearing trumpets, the axes of which are separated about 30 inches. An india-rubber tube proceeding from the axis of each is placed so as to terminate in the ear of the observer--one in each ear. With this instrument the audibility of the sound was very much increased, but as a means of determining the direction of the source of sound, it was apparently of little use. For this purpose the unaided ear is sufficient, provided the head is placed above all obstructions and away from reflections. HOT WATER IN DRESSING ORES. We have before alluded to the investigations made to ascertain the reason why clay settles more rapidly in solutions of some salts than in pure water, a fact which appears contrary to reason, since it might be inferred that the greater the specific gravity the more buoyant the fluid. But the fact is abundantly confirmed, and it is likely to find important application some day in the arts. The property which every substance has of sinking through a fluid of less density than its own forms the basis upon which nine-tenths of the gold and copper, and probably six-tenths of the silver produced in this country, is extracted from its ores. It is the foundation of the art of ore dressing, one of the most important parts of metallurgy. Anything which increases the rapidity and thoroughness of the process may have a fortunate application in this art. Mr. Ramsay, of the Glasgow university laboratory, thinks the property in question depends upon the varying absorption of heat by the different solutions. When water containing suspended clay is heated the rapidity of settling is proportional to the heat of the water. This mode of accelerating the movement of fine sediments in water is perhaps more easily applied than the solution of caustic soda or potash, or of common salt. Rittinger, by a mathematical discussion of the principles which control the downward movement of solid particles in an ascending stream of water, showed that the separation of light from heavy minerals is more complete with solutions of density greater than that of water than in water alone. He found a solution of 1.5 sp. gr. extremely favorable. If the addition of heat will increase the effect of such a solution, it may become possible to