VII. LIGHTHOUSES, ETC. 445 



218Oa. Model of a Propeller for Ships. 



S. F. Pichlcr, London. 



2180b. Model of Bevis's Patent Feathering Screw 

 Propeller. Laird Brothers. 



Mr. 11. 11. 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 as under 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. 



218Oc. First Helmet made for Diving Purposes, date 

 A.D. 1829. Siebc and Gorman. 



218Od. Patent Helmet for Diving, fitted with segmental 

 neck ring and 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. Siebc and Gorman. 



VIII. LIGHTHOUSES AND FOG SIGNALS. 



2181. Model of a Lighthouse built upon the Bishop 

 Rock, 7 miles from land, forming part of the outermost reef 

 S.W. of the Scilly Islands. Trinity House, London. 



The tower is of Cornish granite (Carusew), and is surmounted by a lantern 

 of gun-metal, containing lenticular apparatus to exhibit a fixed light of the 

 first order, whose focal plane is 110 feet above high- water spring tides. The 

 structure measures from base to vane 147 feet. It was built from designs by 

 the late James Walker, M.T.C.E., under the superintendence of Nicholas 

 Douglass, for the Corporation of Trinity House, London, at a cost of 36,500/., 

 and occupied six years in construction ; it was completed in 1853. A sectional 

 drawing shows the method of bracing by vertical and radiating wrought- 

 irou ties, lately adopted for Strengthening the structure. 



