176 THE CORRELATION OF FORCE. 



single radiant point or at least from a surface of very 

 limited extent, such as the oxyhydrogen and the electric 

 light were discovered, it was at once seen that some very 

 great advantages would result from employing these meth 

 ods in light-houses. 



But there are other things to be considered besides the 

 concentration and brilliancy of the light employed for this 

 purpose. The facility of managing it, and the absolute cer- 

 tainty of it that is, its entire exemption from all danger 

 of getting out of order, with the care and attention that 

 a guardian of average skill and fidelity can be relied upon 

 to bestow are points of essential importance. It is not 

 enough, therefore, that a scientific operator in his labora- 

 tory can produce, by ingenious contrivances, a very pow- 

 erful and concentrated light, and one which he can perfect- 

 ly manage and control in a lecture-room for the amusement 

 and instruction of an audience. Before his plan can be 

 adopted by a Light-house Board they must know how his 

 light is produced, what would be the cost of it on a great 

 scale, and whether the apparatus necessary for producing 

 it can be managed safely and certainly by unscientific, 

 though careful and faithful men ; and, more than all, 

 whether there is any possibility that, even so seldom as 

 once in five or ten years, the process of producing it might 

 fail, through some unexpected derangement of the appara- 

 tus or other accident, so as to leave the mariners who might 

 'be on the lookout for it without its warning of their ap- 

 proach to the land for several hours, and perhaps for a 

 whole night. There are, at the present time, about six 

 hundred lights on the English coasts, and if the system 

 was such that a light was liable to be out of order even 

 once in ten years, that would make the number sixty upon 

 the average that would fail during some night of every 

 year. Such an uncertainty as this w 7 ould greatly impair 



