Some Account of the Northern Light-houses. 117 



and the regular system of the Board, are most satisfactorily esta- 

 blished. 



With regard to the characteristic appearance of the Northern 

 Lights, they may be classed as stationary/, revolving; flashing, 

 and intermittent lights. In the first, as its name implies, the 

 light has a steady and uniform appearance, and the reflectors 

 are ranged in circular zones upon a chandelier or piece of iron 

 frame-work, which is either supported upon a pedestal, or sus- 

 pended by truss-work from the roof of the light-room. The 

 revolving light consists of a frame built upon a perpendicular 

 shaft, and the reflectors are ranged on perpendicular planes or 

 faces, which are made to revolve in periodic times, by means of a 

 train of machinery kept in motion by a weight. When one of 

 those illuminated planes or faces is brought round toward the 

 eye of the observer, the light gradually increases to full strength, 

 and again diminishes in the same gradual manner. When, on 

 the contrary, the angle between two of these faces comes round, 

 the observer is in darkness. By these alternate changes, the 

 characteristic of the light-house is as distinctly marked to the 

 eye of the mariner as the opposite extremes of light and dark- 

 ness can make it. The flashi^ig light is a modification of the 

 revolving light, and is practically a beautiful example of the 

 infinite celerity of the passage of light. The reflectors are here 

 also ranged upon a frame, with faces which are made to revolve 

 with considerable rapidity ; and the light thus emerging from a 

 partial state of darkness, exhibits a momentary flash, resembling 

 a star of the first magnitude, and thereby produces a very 

 striking effect. The King of the Netherlands having applied 

 to the Light-house Board for a description of this light, as ap- 

 plicable to some part of the coast of Holland, was graciously 

 pleased, on receiving it, along with a copy of the book now be- 

 fore us, to present the Engineer of the Board with a massive 

 gold medal, bearing his Majesty's effigy, with a suitable inscrip- 

 tion upon the reverse. Similar applications with regard to the 

 flashing light have been more recently made from other quar- 

 ters. The intermittent light suddenly appears like a star of the 

 first magnitude, and contmues as a stationary light a minute and 

 a half, when it is as suddenly eclipsed for half a minute, and, 

 by this simple arrangement, a strongly marked distinction in 

 the lights of the coast is introduced. This is accomplished by 



