NAVIGATION. 127 



the state of the atmosphere, the light of a power- 

 ful oil lamp is insufficient. In the system of short 

 and long eclipses, the signal lamp is allowed 

 to show its light uninterruptedly until the signal 

 commences. Then groups of long and short 

 eclipses the short eclipses of about half a second's 

 duration, the long eclipses three half seconds, the 

 interval or intervals of brightness between the 

 eclipses of a group half a second ; such groups, I 

 say, of long and short eclipses are produced by a 

 movable screen, worked by the sender of the 

 message, and read off as letters, numerals, or code 

 signals by the receiver or receivers. Experience 

 shows that a person, familiar with the flash method, 

 can, without further practice, read off the eclipses 

 with equal ease, and vice versa ; and, when it is ad- 

 visable to use the magnesium lamp, both sender and 

 receivers will be equally quick and sure in their use 

 of it if they ordinarily use the eclipse method instead 

 of, as now in the navy, the method of long and short 

 flashes. Whenever the light of a lamp suffices, 

 the eclipse method is decidedly surer, particularly 

 at quick speeds of working, than the flash method, 



