H. R. CARLETON. XCIX. 



flame is about six inches, and great heat is given off, special care 

 being necessary to prevent breakage of the glass chimney. 

 Mineral oil is chiefly used in New South Wales, and the oil is 

 made to flow into the burners by various means. Fresnel's in- 

 vention consisted of four small pumps worked by clockwork 

 which forced the oil upwards to the flame. Other modes are by 

 weights acting on a piston, by a spring doing the same office, in 

 the pneumatic lamp by means of the pressure of air in the 

 reservoir, and another plan is by placing the reservoir slightly 

 higher than the lamp, the oil thus flowing freely by gravity to 

 the required level. 



Characteristics. 



The increase of lights naturally leads to the necessity of dis- 

 tinction between them. What is required is a well defined and 

 easily recognised light. The main distinctions are Fixed and 

 Revolving. Fixed, though less powerful than Revolving, is a 

 useful distinction, as coloured sections can be shown from it to 

 indicate dangers in the neighbourhood. With a Revolving light 

 this cannot be effected, but Revolving lights are more distinctive 

 than Fixed lights, the alternations of light and darkness are so 

 marked as to strike the most careless observer. The tendency of 

 late has been in the direction of shortening the interval of dark- 

 ness, very few of the longest periods being now more than a 

 minute, for with the iucreased speed of steamships a considerable 

 distance might be traversed before the full character of a long 

 period light could be made out. The characteristics in use are : — 

 1. Fixed. 2. Revolving light, gradually increasing at equal 

 periods to full power, and then gradually decreasing to eclipse. 

 3. Fixed lights, varied by flashes ; shows a fixed light which at 

 certain periods is varied by white or coloured flashes. 4. Flash- 

 ing, shows a single flash at intervals of a few. seconds. 5. Group 

 Flashing, shows groups of two or more flashes in quick succession, 

 separated by a period of eclipse between the groups. 6. Inter- 

 mittent, which bursts instantaneously into full power, and, after 

 remaining for a period as a fixed light, is suddenly eclipsed. 



