The last files of the Sydney Morning Herald contain accounts of a new propeller invented by Sir Thomas Mitchell, the Surveyor General of New South Wales, a trial of which in a small steamer at that port had just excited great interest. It is called the Bomerang Propeller, and is constructed on the principle of the weapon of that name used by the natives to kill game. Although the experiment was only on a small and imperfect scale, a speed of 12 knots an hour against a head wind is stated to have been obtained. The instrument -is 4e*enfce4.j>o combine great strength and simplicity, wile it has also ifa* advantage that its motion in the water causes but a comparatively slight agitation, so that it is capable ot being adapted to canal boats as well as to other vessels. At the conclusion of the trial Sir Thomas Mitchell expressed his conviction " that the weapon of the earliest inhabitants of Australia has now led to the determination mathematically of the true form by which alone, on the screw principle, high speed on water can be obtained