MARINE LIGHTING EQUIPMENT OF THE PANAMA CANAL. iii 



of ground glass elements are now used in all modern lighthouse apparatus, 

 the system employed for buoys being known as the Dioptric System, in 

 which the light from the luminous source is collected and caused to travel 

 along a horizontal plane by refraction (see Plate 54). The sixth order 

 (300 mm.) Fresnel lenses for the Panama buoys are composed of nine separate 

 elements, cemented together and held securely by a brass frame of helical bars. 



To secure the maximum efficiency from the lens, the vertical bars of 

 all standard buoy and beacon lanterns are equipped on their inner side with 

 totally reflecting glass prisms, arranged so that the light which falls on any 

 one prism is reflected out into the shadow caused by the adjacent bar (see 

 Plate 55). 



By a patented device, all of the light which emanates from the lens is 

 affectively turned to account and uniformly spread throughout the complete 

 horizontal plane, whereas in all other types of lanterns much of this light 

 is obstructed by the bars and lost. The lantern consists of three principal 

 parts, viz., the hood, the central belt, and the base (see Plate 49). 



The hood, which is made of sheet copper, serves for ventilation, its 

 construction rendering the lantern absolutely storm-proof, that is, making it 

 impossible for wind or sea to extinguish the light. 



The central belt is provided with storm glasses, through which the light 

 shines. These glasses are held in place by vertical bars, equipped with 

 reflecting prisms, as described above. 



The base contains the flasher and governor, which are securely fastened 

 with screws to the bottom plate. 



Into this base is secured the lantern and pressure-gauge valve referred 

 to on a previous page, and when required (as for beacons) a cock is fitted 

 for use in connection with the sunvalve. 



Although not employed on buoys, it may be of interest in concluding 

 this paper to give a brief description of the sunvalve, the invention of the 

 Swedish engineer, Gustaf Dalen. 



THE SUNVALVE. 



The sunvalve (Plate 56) controls the flow of gas to the burner so that 

 the light will burn and gas be consumed only when actually required, that 

 is, during darkness, thus effecting great fuel economy and increasing the 

 service capacity of the accumulators. It is actuated entirely by light, and 

 operates quite independently of temperature, so that it may be employed 

 in any climate of the world. For example, many of the lights established 

 by the United States Lighthouse Bureau in northern Alaska are equipped 

 with sunvalve, also in the Hawaiian Islands and other tropical countries this 



