440 Sir James N. Douglass [Marcli 15, 



observers, trained and untrained, scientific and practical. The report 

 of the Committee was presented to both Houses of Parliament, by 

 command of Her Majesty, in 1885. The final conclusions of the 

 Committee are given in the following words : " That for the ordinary 

 necessities of lighthouse illumination, mineral oil is the most suitable 

 and economical illuminant, and that for salient headlands, important 

 landfalls, and places where a very powerful light is required, elec- 

 tricity ofiers the greatest advantages." 



I have already referred to the necessity, with the present develop- 

 ment of maritime commerce, that every beacon light maintain a 

 clearly distinctive character. When the optically unaided flames of 

 coal fires were the illuminants of our lighthouses, distinctive cha- 

 racters, owing to the small number of lights then employed, were of 

 little importance, and the only distinctions then j)ossible were the 

 costly ones of single, double, or triple lighthouses at one station ; 

 but with the enormous increase that has since occurred in the floating 

 commerce of the world, and with the necessary laws now in operation 

 requiring all vessels to carry lights, trustworthy individuality in 

 coast beacon lights has become a positive necessity. Until very 

 recently the distinctive characters consisted of the following : viz. — 

 fixed white, fixed red, revolving white, revolving red, and revolving 

 white and red alternately. The revolving lights showed a flash at 

 periods of 10 seconds, 20 seconds, 30 seconds, one minute, 2 minutes, 

 3 minutes, and 4 minutes. There were also intermittent or occulting 

 lights, having an eclipse at periods of half-a-minute, one minute, or 

 2 minutes. It is now generally considered that fixed lights are no 

 longer trustworthy coast signals, owing to their liability to confusion 

 with other lights, both ashore and afloat. It is also considered that 

 in these days of high speed vessels the period of the character of a 

 coast light should not if possible exceed half-a-minute. The revolving 

 or flashing class of lights are probably the most valuable, on account 

 of their superior intensity, as compared with the fixed or occulting 

 class, the light during the intervals of eclipse being condensed into 

 each succeeding flash by the revolving lenses or reflectors, and thus, 

 with the same expenditure of the illuminant, an intensity is obtained 

 in the flashes of five to eight times that of the fixed or occulting 

 class. Where local dangers are required to be guarded by coloured 

 sectors of danger light with well-defined limits, this can only be 

 accomplished with the fixed or occulting class of lights. We will 

 illustrate this with the model before us. We will also show the clear 

 difierence of character, not generally realised, between flashing and 

 occulting lights. A system of occulting lights for lighthouses was 

 proposed by the late Charles Babbage, F.E.S. in 1857 ; but as it 

 excluded the flashing or most powerful of the existing lights, it 

 did not receive much favour from lighthouse authorities. And in 

 1872, ' Distinctive Characters for Coast Lights,' was the subject 

 of a paper by Sir William Thomson, F.R.S. at the Brighton Meeting 



