108 ANNUAL OF SCIENTIFIC DISCOVERY. 



medium would take effect ; that is, the motion of revolution of the 

 moon will be accelerated, and the rotation of the earth retarded, till 

 the day and tfhe lunar month become equal. 



The action of such a cause is traceable in the rotation of the moon 

 on its axis. It is well known that our satellite has always, since the 

 earliest records of its appearance, presented the same face to the 

 earth. It is in the highest degree improbable that its rotary motion 

 was in the beginning exactly adjusted so as to produce this effect. 

 But if the moon were liquid, or covered by a liquid, the immense 

 tides produced by the earth would in time produce the effect which 

 we now see. The hypothesis that the equality in the times of revo- 

 lution and of rotation of the moon is to be attributed to this cause, 

 derives additional strength from the fact that the satellites of Jupiter 

 seem to follow the same law. This equality, once established, will 

 continue forever. In consequence of the acceleration of the moon's 

 motion, and the consequent diminution of the lunar month, she will, 

 in a few thousand years, be half a month ahead of the place in which 

 she would be if her month were to remain constant, and will, there- 

 fore, be on the opposite side of the earth. If her time of rotation 

 remained constant during that period, the side which is now hidden 

 would then be presented toward the earth, so that our posterity of 

 two hundred centuries hence would have an opportunity of unveiling 

 its mysteries. But analysis has answered the question for them, and 

 demonstrated to us that the hemisphere of our satellite, which is now 

 turned from the earth, will so remain, hidden from mortal eyes, to 

 eternity. 



Viewing the system of the world, then, with the aid of all the light 

 that can be thrown on it by science and by philosophy, selecting the 

 most probable causes for those phenomena of nature which we can- 

 not deduce from the known general laws of the universe, and tracing 

 these and all known causes to their most remote and latent effects, 

 making at every step all due allowance for our ignorance, and giving 

 proper weight to every sound philosophical principle which bears on 

 either side, there seems to be a decided preponderance of evidence 

 in favor of the doctrine that this system is not entirely self-sustaining 

 and self-compensating, but is subject to actions which must lead to its 

 ultimate subversion. North American Review. 



THE ELECTRIC LAMP IN LIGHTHOUSES. 



For the last five or six years the maritime world has been waiting 

 with some anxiety for the termination of some experiments respect- 

 ing the employment of the electric light as a beacon. These experi- 

 ments are well-nigh concluded, and the question whether the old oil- 

 lamp is to be superseded by the electric lamp will be speedily deter- 

 mined. 



Early in 1857, experiments were made on the subject by Prof. 

 Faraday and Prof. Holmes, and subsequently the latter was re- 

 quested by the Trinity House to prepare a plan for employing the 

 new light. This plan was submitted to Prof. Faraday, who reported 

 favorably upon it, and the result was that the Trinity Board sanc- 

 tioned the establishment of an electrical apparatus in the South Fore- 

 land Upper Lighthouse, This apparatus consisted of an accumulation 



