LIGHTHOUSE ILLUMINATION. 



BY PROFESSOR T. F PIGOT 



THE subject we have to take up to-day is that of light- 

 houses, or rather the illuminating portion of lighthouses, 

 with a description of the apparatus used for this purpose, 

 which is exhibited in this collection. 



Lighthouses have for their object to direct the course of 

 vessels at night, sometimes warning them off dangerous 

 points, whether reefs, rocks, or sandbanks, sometimes 

 guiding them in the direction of a channel they have to 

 follow. 



Hence it will be at once clear that light thrown upwards, 

 above the horizon, and light thrown downwards, towards 

 the base of a lighthouse, would be of no use whatever. 



In lighthouses built on land, the land side does not 

 require to be illuminated, and even when built on rocks or 

 reefs at sea they are generally not very far from land, and 

 in that direction their illuminating power does not require 

 to be so strong as towards the sea. 



Thus it is that apparatus serving to utilise the upward 

 and downward rays of a lighthouse lamp by diverting 

 them to the best direction for mariners must be advanta- 

 geous ; and further, if by any means, the rays towards the 

 land can be utilised for strengthening the seaward light, or 

 in giving greater intensity of light to certain required arcs 

 in azimuth, say in the direction of a channel, there will be 

 a gain to mariners of all that light which would otherwise 

 be wasted. 



