MECHANICS AND USEFUL ARTS. 33 



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in the slightest current of water or air, greater simplicity and power, its 

 adaptation to attain any velocity required, high or low, and that it -will 

 propel a vessel from 50 to 100 per cent, further, in the same period, with 

 less fuel consumed, than screws of the ordinary construction. They also 

 work more kindly than the ordinary propellers, are not likely to receive 

 injury at sea, and can not get foul of sunken ropes or chains from the ships hi 

 rivers. 



In a discussion at the last meeting of the British Association on the effects 

 of screw-propellers, when moved at different velocities and depths, Mr. Gr. 

 Rennie stated, that from, experiments which had been made under his observ- 

 ation, it was desirable that the screws of vessels should be of small dimen- 

 sions, light, and of rapid motion, and that their effect would be increased by 

 their being as deeply immersed as possible. He also recommended the disc 

 screw. 



Improvements in Masts. An iron screw-steamer, of 600 tons, recently built 

 at Glasgow, Scotland, for the African Steamship Company, has her mainmast, 

 from step to several feet above upper deck, of a strong iron tube, into which 

 is fitted the usual wooden mast. By this means, should the mast break, or 

 be cut away, a new one can easily be fitted in without disturbing the cargo. 

 This vessel has also her keel built on a plan patented some time ago, having, 

 instead of a solid forged bar, several plates securely riveted together, thereby 

 giving a great increase of strength at less cost. 



Supporting Ships' Topmasts. Ordinarily, the lower end of a ship's topmast 

 is supported on what is known, in nautical parlance, as a "fid." This consists 

 of a square bar of -iron, which passes through the heel of the topmast, at 

 right angles to the latter. The "fid" rests on the "trestle-trees," which are 

 two stout horizontally projecting pieces, secured near the top of the lower 

 mast. In all vessels there is more or less tendency in the "trestle-trees" to 

 sag down out of a horizontal position, for upon them falls the entire weight 

 of the topmasts, with all their spars, sails, and rigging. It is no easy matter 

 to restore the topmasts to their proper position when once the "trestle-trees" 

 have given way. Thomas Batty, of Brooklyn, K Y., by a method recently 

 patented, supports the topmast by providing two iron straps, which extend 

 on an angle, from the cap of a lower mast to the ends of a bolt that passes 

 through the heel of the topmast and answers as a "fid." The heel is also 

 furnished with a strong iron thimble. Both straps are made in two pieces, 

 united at their centers by nut and screw ; whenever it becomes necessary to 

 raise the heel of the topmast, it may be done in a moment by screwing up 

 the straps. Scientific American. 



STOEM-AXCHOE. 



Mr. R. D. Guinon, of Brooklyn, N. Y., has patented a very simple and ob- 

 vious improvement on, or rather attachment to, the common ship's anchor, 

 designed to give it a better holding power in a muddy or quicksand bottom. 

 The chief characteristic of an anchor, like that of the miser's soul, is its ten- 

 acious hold on "things of earth." and. singularly enough, its steadfast charac- 



