curious.--_La Nature_. * * * * * MERCURY WEIGHING MACHINE. We illustrate herewith a novel type of weighing machine. Hitherto the weighing machines in common use have either been designed with some kind of steelyard apparatus, upon which weights could be moved to different distances from a fixed fulcrum, or springs have been so applied as to be compressed to different degrees by different weights put upon the scale pan, or table, of the machine. In other instances more complicated mechanism is used, and various movable counterpoises are usually required in order to balance the moving parts of the machine. [Illustration] The type of machine which we now illustrate has been recently brought out by Mr. G.E. Rutter, and the system has given very satisfactory results with platform weighing machines. The engraving illustrates a form of balance which may be applied to strength testing machines, or for any work where an apparatus of the type of a Salter's balance would be of use. It is simple in construction, and consists of a tube A closed at the bottom and forming a reservoir for mercury. The body which it is required to weigh is hung upon the hook B carried by the crossbar C, which is connected by rigid rods to the upper part of the tube, and by means of the internal rods D is attached to the cross head E, which works freely inside the tube A. The top part of the tube is, as will be clearly understood from the illustration, cut away to allow of the descent of the rods. To the cross head E is attached the piston F, which may be made of wood or of a hollow metal tube closed at the end, or other suitable material. It will be easily understood that when a weight is hung upon the hook B, the piston F is caused to descend into the mercury which rises in the annular space between the piston and the tube. The weight of the volume of displaced mercury is proportional to the weight of the body hung upon the hook, and the buoyancy of the piston in the mercury forms the upward force which balances the downward pull of gravity. When the apparatus is at rest the piston F descends into the mercury to such a distance as will balance the weight of the rods, hook, and piston itself. If, now, the cross bar G, provided with a pointer H, be fixed to the rods, it should at that time register zero, upon the scale J fixed to the outside of the tube, and as the descent of the piston into the mercury is directly proportional to the weight of the body attached to the hook B, the divisions of the scale will all be equal. It will thus be seen that the apparatus is extremely simple in theory, and it only remains to construct it in such a form that the mercury may not easily be spilt in moving the instrument from place to place. This is effected by causing the cross head E to fill the tube while working freely therein, and a small valve is arranged to allow for the passage of air. The cross bar G can be regulated upon the rods by means of set