42 ANNUAL OF SCIENTIFIC DISCOVERY. 



remarkably small, and, to a casual observer, appear totally inadequate 

 to the propulsion of a boat of such great length ; this, however, we 

 are assured is not the case. 



STEAMBOAT PROPELLERS. 



THERE have been brought to light, recently, two new inventions : 

 the one adapted to give increased speed to screw, the other to paddle 

 navigation. Mr. G. Bovill's screw propeller, described in the Mining 

 Journal, is an entirely novel affair. Its central portion is fitted up 

 with a hollow sphere, occupying one-third of the entire diameter of 

 the propeller, and the blades are made narrower at the outer extrem- 

 ity than at the base. The blades are also made to revolve, so as to 

 admit of the pitch being altered to meet the various circumstances of 

 speed and power. From a table of the comparative result of trials 

 on three different boats, it appeared that important advantages have 

 been obtained from the new propeller. 



The paddle invention is that of a Liverpool shipwright named 

 Hampson. A piece of wood, perhaps about a foot square, and con- 

 nected to a movable framework, so as to be capable of being moved 

 to and fro, was fixed to the stern of the boat ; the paddle, so to speak, 

 being covered by the water, and assuming a slightly diagonal position. 

 By moving two handles rapidly with his hands in the direction of his 

 body from the stern, Mr. H. brought the paddle in rapid motion, 

 the action resembling that of the fin of a fish, the result being to pro- 

 pel the boat with great speed through the water. Mr. Hampson 

 contends, that by this simple appliance alone he can propel row-boats 

 at much more than their ordinary speed, and with infinitely less 

 manual labor; but his grand object is to apply it to sea-going vessels 

 by means of steam and machinery. 



The Sidney papers 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 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 1 2 knots an hour against a head- wind -is stated to 

 have been obtained. The instrument is described to combine great 

 strength and simplicity, while it has also the advantage that its motion 

 in the water causes but a comparatively slight agitation, so that it is 

 capable of being adapted to canal boats as well as to other vessels. 

 At the conclusion of the trial Sir Thomas Mitchell expressed his con- 

 viction " 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." 



