THE EVOLUTION OF THE LIGHTSHIP. 113 



on watch and the emergency fog bell. The latter is used when the steam fog signal 

 is out of order. The forward deck-house supports the bridge and is fitted as a 

 general chart and watch house ; the after house is given over exclusively to the radio 

 outfit. Two boats are carried in cradles on the spar deck as shown. 



The outboard of the vessel is shown in both the photograph of Plate 53 and 

 the drawings of Plate 59. The chief characteristic and distinguishing mark, 

 aside from the unusual sheer and freeboard, lies in the steel tubular foremast which 

 carries a cylindrical lantern at its head for the protection of the signal light. The 

 necessary rig is fitted for three sails, and topmasts are fitted from which a radio 

 antenna is swung at an elevation of 82 feet above the water. 



The signal light consists of a fourth order lens carried upon a compound pen- 

 dulum mounted upon gimbals in the lantern as shown on Plate 60. The adjustment 

 of the top and bottom counterweights on the pendular apparatus, which is some 

 9 feet 6 inches in height, enables a period of oscillation to be obtained much longer 

 than that of the vessel itself, and the extreme movement of the vessel itself is trans- 

 mitted to the pendulum in but a slight degree. The Jens, therefore, stands quite 

 steadily upright and shows a beam of light truly to the horizon except under ab- 

 normal conditions. A fixed white light is shown, which is obtained by an incan- 

 descent oil vapor lamp. This lamp consists of a reservoir of kerosene under a 

 pressure of about 60 pounds, which ejects the oil through a heating tube, where it 

 is vaporized and from which it is thrown as a vapor upon a mantle which becomes 

 incandescent under the heat of the flame. 



More recent installation of similar pendular apparatus, made upon older ves- 

 sels undergoing repairs, has the gimbal suspension made up of knife edges, and 

 much more sensitive adjustment and correspondingly greater steadiness are thereby 

 obtained. Such installations have also been successfully fitted with electric lights. 



The main propelling engine consists of one vertical, direct-acting, open-front, 

 surface-condensing, fore-and-aft compound engine, with cylinders 16 inches and 

 31 inches in diameter, and a piston stroke of 24 inches, as shown in Plate 61. 



Steam is furnished by two boilers of the Scotch type, Plate 62, 10 feet 6 inches 

 mean diameter and 11 feet 4 inches long, carrying a working pressure of no 

 pounds per square inch. The propeller is of cast steel with four blades, 8 feet in 

 diameter and with 10 feet pitch. On trial the vessel steamed at 9.9 knots with 380 

 indicated horse-power, and readily developed a speed of 9^ knots under normal 

 conditions with an indicated horse-power of 300. 



The performance of the vessel upon its station has been most satisfactory 

 and with a metacentric height ranging from 17 inches to 9 inches between the full 

 load and light conditions, a duration of period and range of movement has been ob- 

 tained which is most satisfactory. The high topsides also render the vessel sea- 

 worthy under extreme conditions, and the indications of the curves of statical and 

 dynamical stability shown in Plate 63 are found to be fully realized in service. 



