IMPKOVEMENTS IN COAST SIGNALS.' 585 



haustive series of experiments is now being carried out by the Trinity 

 House at the South Foreland with mineral oil, coal and oil gas, and 

 electric arc luminaries, for the purpose of determining the exact relative 

 efficiency and economy of the three illuminants for coast lighting. The 

 results of this important investigation are looked forward to with great 

 interest, as marking an important epoch in the progress of coast lighting. 



It is evident that the responsibility for reliable individuality in coast 

 signals increases with the development of trade along any line of coast, 

 more especially since light and sound signals are compulsorily carried by 

 all vessels, whether steam or sailing. 



A system of occulting coast signal lights was proposed by the late 

 Charles Babbage, F.R.S., in 1851, but, unfortunately, the system excluded 

 the most powerful and efficient of the existing lights, viz.. the revolving 

 or flashing class, whose intensity averages about five times that of the 

 fixed light, and thus Babbage's proposal lay nearly dormant for many 

 years. The subject was brought before the British Association by Sir 

 William Thomson, LL.D., F.R.S., at the Brighton meeting in 1872. when 

 he drew the attention of the Association to the extreme importance of 

 ready identification of lights at sea, and proposed the use of flashing 

 lights, their flashes being of longer or shorter duration ; the short and 

 long flashes representing the dot and dash of the Morse alphabet as used 

 in telegraphy. 



Until very recently the distinctive characters of coast signal lights 

 consisted of the following — viz., fixed white, fixed red, revolving white, 

 revolving red, revolving alternate white and red. The revolving lights 

 showed a flash at periods of 10 seconds, 20 seconds, 30 seconds, 1 minute, 

 2 minutes, 8 minutes, and 4 minutes. There were also intermittent or 

 occulting lights having an eclipse at periods of h minute, 1 minute, or 2 

 minutes. It is now generally conceded that fixed lights are no longer 

 to be considered as trustworthy coast signals, owing to their liability to 

 confusion with other lights, both ashore and afloat. It is also generally 

 conceded that the period of a coast signal light should not exceed half a 

 minute ; further, that time should not form an element in the determina- 

 tion of the distinctive character of a coast signal. On the coast of Eng- 

 land the Trinity House are converting as rapidly as practicable all fixed 

 lights to occulting, where local dangers are required to be covered with a 

 red sector or sectors of danger light. In cases where this local mapping 

 out of dangers is not required, flashing lights, in consequence of their 

 higher intensity, are being adopted. 



The electric arc light is eminently efficient for the occulting class of 

 lights with red sectors, owing to the very sharp and perfectly defined lines 

 of demarcation that are capable cf being produced between the sectors 

 with a luminary so small and compact at the focus of the optical apparatus. 



The French Commission des Phares have lately had under considera- 

 tion a complete system of electric light and sound signals for the coast 

 of France. They have agreed to abolish as far as possible fixed lights, 

 and they have determined that time shall not be considered an element 

 in the identification of flashing lights. The following code of flashing 

 lights, having periods of about ten seconds, proposed by M. Allard, late 

 Inspector- General of the French Lighthouses, has been adopted for the 

 proposed electric lights when substituted for the existing oil lights, viz., 



Single flashing. 



Double flashing. 



