A New System for Preventing Collisions at Sea 



apparatus, and the record thus made will give us a fair idea 

 of the object struck. It will indicate its size and shape 

 with a fair degree of accuracy ; it will indicate its direction 

 from the ship, and will also show its distance with great 

 accuracy. It will distinguish a ship from an iceberg, will 

 show whether the object is stationary or moving, and if 

 moving the direction and velocity of such movement. 



Before describing fully the modus operandi of this apparatus, 

 we will first examine some of the phenomena relating to sound 

 and the accompanying echo. 



On one occasion I witnessed a stroke of lightning at a 

 distance of ten feet. It was simply a blinding flash and a 

 short, sharp, ear-piercing snap ; I did not hear any thunder. 

 The duration of a flash of lightning is only a small fraction 

 of one-thousandth part of a second, and still we hear the 

 thunder roll for some seconds, perhaps ten or more. All the 

 noise is produced in less than one-thousandth part of a second. 

 The thunder is not the direct sound, but the echo, which varies 

 greatly, according to the character and distance of the object 

 that reflects the primary sound. On one occasion, while on 

 the very roughest part of the Tete Noire, we were overtaken 

 by a very violent and noisy thunderstorm. There were many 

 large objects all around us, and each flash of lightning was 

 followed by noises coming from all directions and resembling 

 musketry fire. The clatter was so great that I failed to hear 

 a " thunder roll " of the kind so well known in all level 

 countries and at sea. The rolling and reverberating sound 

 known as thunder that follows a lightning flash is all made 

 up of echoes. The first short sharp primary snap sends out 

 vibrations that strike the clouds ; if the clouds were solid and 



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