IX. NAVAL AKCHITECTURE, ETC. 531 



21 SOb. Model of Bevis's Patent Feathering Screw 

 Propeller. Laird Brothers. 



Mr. II. K. Bevis, managing engineer to the firm of Messrs. Laird Brothers, 

 of Birkenhead, in 1868 patented an arrangement for altering the pitch or 

 feathering the blades of a screw propeller in a fore and aft direction, which 

 claims to be a great advantage for screw steamers, making them faster and 

 more handy when under sail alone, and when under steam and sail allowing 

 of adjusting the pitch to obtain the best result. A screw propeller of the 

 ordinary kind, whether fixed or revolving, is a heavy drag against speed and 

 handiness for sailing, and " lifting " it is a laborious operation, and requires 

 a large hole or well through the ship's counter to admit of so doing. 



The arrangement of this new screw propeller is free from many of the 

 objections which have been made to feathering screws previously tried. The 

 gear for feathering the blades is well protected, the levers and other gear that 

 move the blades being enclosed within the boss of the screw propeller, and 

 attached to a rod passing through the centre of the shaft, which is worked in the 

 screw shaft tunnel. This system is admirably adapted for ships of war or sailing 

 ships with auxiliary power or yachts, where it is as important to have a good 

 result under sail alone asunder steam. The operation of altering the pitch, or 

 of feathering the blades to any angle, is done in a few minutes, without in 

 any way putting the engines into a position that they may not be used in an 

 emergency. 



This feathering propeller has now been successfully tried in 15 vessels, and 

 is at present being fitted to four vessels of H.M. Navy, one of them of 2,100 

 ind. horse-power. 



2180c. First Helmet made for Diving Purposes, date 

 A.D. 1829. Siebe and Gorman. 



2180d. Patent Helmet for Diving, fitted with segmental 

 neck ring find safety locking arrangement, inflating valve for 

 bringing diver to the surface. Fitted with speaking apparatus to 

 enable the diver to communicate with his attendant. Used on 

 board H.M. Ships of the Royal Navy. Siebe and Gorman. 



2180e. Diving Spectacles, fitted with air-lenses, having a 

 focus in water of I}? inch, for subaqueous vision. 



R. E. Dudgeon, M.D. 



The air-lenses are prepared from two sections of a thin glass globe 1^ inch in 

 diameter, fixed in a spectacle frame with their convexities towards one another, 

 and their concavities outwards. Underwater these spectacles have a focus of 

 1^ inch, and supply the refractive power lost by the eye when submersed in 

 water, owing to the aqueous humour which forms the anterior lens of the eye 

 having the same index of refraction as water. Exhibited in the International 

 Exhibition of 1871. 



218Of. Boat moved by A. H. Gar rod's Undulating 

 Propeller. H. C. Ahrbecker. 



This model is moved by an undulating propeller, of which the component 

 staves (which carry the undulating membrane) successively receive their 

 transverse motion from the rotation of a screw with which they are in lateral 

 contact. 



Invented by A. H. Garrod, in imitation of the undulating propelling fins of 

 the pipe fish and sea horses. 



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