REFLECTION OF LIGHT. 



157 



being set down in a cottage window to guide a 

 husband to his home, but when we want to 

 make a similar guide on a large scale, not 

 merely over a river or over a moor, but over 

 large expanses of sea, how can we then make 

 the signal using only a candle ? I have shown 

 in this diagram (fig. 55) what we may imagine 



Fig. 55. 



to be the rays of a candle or any other source 

 of light emanating from the centre of a sphere 

 in all directions round to infinite distances. 

 After this simple kind of light had been used 

 for some time, it being found to be liable to be 

 obscured by fogs, or distance, or other circum- 

 stance, there arose the attempt to make larger 



