March 1st, 1S87.] 



SCIENTIFIC NEWS. 



ELECTRIC LIGHT FOR NAVIGATION. 



IT has recently been reported that the capacity of the Suez 

 Canal for traffic has been almost doubled since it has 

 been lighted with arc lamps. In fact, in this great highway 

 of the eastern and western nations, ships can now pass to 

 and fro at night without more risk than in the daytime. It 

 is also admitted by Sir James Douglass, the Engineer of the 

 Trinity Board, and by other high authorities, that arc lights 

 are, in many cases, the best for lighthouse illumination, be- 

 cause the light can be so clearly seen at very long distances. 

 Moreover it is now a common practice to fit arc lamps for 



Fig. I. 



search lights in harbours and forts, and on board war ships, 

 to guard against approaching vessels. 



It will therefore be seen that the electric light has already 

 lent itself to some very important applications connected 

 with navigation by night, and the question naturally presents 

 itsell : Cannot it also be used for head- lights in ships of all 

 kinds, so that collisions may be more easily avoided ? The 

 great power and range of the arc light are beyond doubt, and, 

 as, by its means, an approaching vessel can be detected at a 

 great distance, the answer eventually will doubtless be in 

 the affirmative. In so important a matter, however, it is 

 not only desirable, but essential, that all that can be said for 

 and against the use of Llcrtm lit^ht In- such a purpose 



Fig. 2. 



should be carefully considered, and we shall welcome any 

 correspondence from competent persons on the subject. 



It is urged that in a strong beam of light the clearest 

 atmosphere is bright with reflecting particles, which, to a 

 certain extent, produce an appearance of mist or fog, and 

 that if the arc light be placed so that the projected beam is 

 above or on the same level as the steersman or look-out 

 man, he must either look through the beam or along it, and 

 so be more or less dazzled by it and unable to discern 

 objects not immediately in the path of light. Similarly the 

 men on the look-out in the vessel approaching the electric 

 light will be dazzled ; and further, that as they are not 

 accustomed to such a light, they will miscalculate the 



distance between the two vessels. We are, however, glad 

 to be informed by the Anglo-American Brush Electric Light 

 Corporation that, after careful trials, they have proved that 

 if the lamp be placed below the line ol vision of the observer, 

 and so focusscd that the beam of light is not only well 

 spread laterally, but is at the same time kept on the surface 

 of the water, the above objections are avoided. The accom- 

 panj'ing Fig. i shows the lantern used by the Brush 

 Company, and Fig. 2 represents its effect when in use. The 

 arrangement consists essentially of a lantern enclosing an 

 arc lamp, having a nominal pS'^'er of about 6,000 candles. 

 A parabolic reflector is fitted in the back of the lantern, and 

 the beam reflected from it passes through a dispersion lens, 

 which causes the beam to be widened in the ratio of i to 10; 

 for example, at a distance of 500 yards it is about 50 yards 

 wide, and at a distance of 1,000 yards, 100 yards wide. 



It is assumed that by this arrangement the beam of light 

 will always be kept below the look-out men on either of 

 two approaching vessels, but it should be remembered that 

 each vessel will roll and pitch, and it does not appear to us 

 conclusive that motion of this kind will not, to a certain 

 extent, make good some of the objections urged against the 

 use of electric light for this purpose. However, we cordially 

 wish it success, and shall he pleased to hear that all reason- 

 able objections have been entirely disposed of, as there is 

 no concealing the fact that as the number and speed of 

 steamers increase, there is an increasing need for avoiding 

 the disastrous collisions with which we arc but too familiar. 

 Moreover, if electric light is used in the way suggested, 

 there will be the further gain that, as a powerful beam will 

 precede the ship, there will be much less risk of the latter 

 being run on to a projecting rock or headland when coasting 

 round a dangerous shore. In all steamers there is ample 

 steam power to spare for driving the electrical machine, 

 and when glow lamps are used for the saloons and cabins 

 the same dynamo can be used for the head-light. 



Boiler Explosions. — M. Hocherau has started a very 

 novel theory of the cause of boiler explosions. It appears 

 that he attributes them chiefly to the presence of gas and 

 air in the boiler, and to the firing of this mixture by means 

 of an electric spark. He supposes that hydrogen, or carbu- 

 retted hydrogen, is readily produced when the water in the 

 boiler cr.iitains organic substances, especially fats, which are 



decomposed on being heated. We all know that air held in 

 solution by the water is driven off in the process of ebulli- 

 tion, and this, he supposes, forms an explosive mixture with 

 the gas, and it only remains to be seen how it can be fired. 

 M. Hocherau's theory is that an electric spark may be formed 

 by the friction of globes of steam in narrow passages, and he 

 infers that the most dangerous moment is when the engine 

 is started. This view he supports by showing that out of 

 twenty-four marine boilers in which explosions had occurred, 

 four exploded when the piston had reached the end of the 

 stroke, and nineteen when the engines were started. Prac- 

 tical men will be unlikely to accept this remarkable theory 

 without further confirmation. 



