July 20, 1888.] 



SCIENTIFIC NEWS. 



57 



SPECTRO-TELEGRAPHY. 



SPECTRO-TELEGRAPHY is the name of a new inven- 

 tion by Paul la Cour, the inventor of the phonic wheel, 

 and its synchronism for multiplex telegraphy. The instru- 

 ments are shown at work at the present moment in the 

 Copenhagen Industrial Exhibition, and the invention, which 

 is patented, is based upon quite a new principle. It may 

 be used for several purposes, but I shall here confine 

 myself to pointing out and describing in detail the appli- 

 cation of the system to nautical use as a simple means of 

 communication from lighthouse to ship, and vice versa, 

 and between ships themselves. 



It is well known that such a signal system exists, but 

 it is only available in the daytime. The first idea was 

 originated in England, in 1857, it was taken up by 

 France, and afterwards by nearly all maritime nations, 

 and is known as the international flag system. Generally 

 speaking, the signals are not meant to express words 

 and sentences by spelling, but only to give a limited, 

 though very large number of sentences, which are 

 arranged in a signal book (international code of signals). 

 It has the advantage, however, that each vessel can carry 



Fig. 1. 



Fie. 



a signal-book in its own language, and two ships of 

 different nationalities are thus enabled to correspond 

 without understanding each other's language. 



The signalling is accomplished by means of 18 flags 

 and pennants, each of which indicates one of the letters, 

 B, C, D, F, G, H, J, K, L, M, N, P, Q, R, S, T, V, W. 

 Of these are then formed two, three, or four- flags signals, 

 respectively, in the number of 306, 4,896, and 73,440. 

 All the two and three-flags signals and the first 18,960 

 of the four flags are intended for the different communi- 

 cations, queries, and answers. The others are reserved 

 as " distinguishing signals " for ships, 1,440 for men-of- 

 war, and 53,040 for trading vessels. 



The large extension which this system has attained in 

 a comparatively short period is a proof of its practical 

 arrangement ; still it has one disadvantage, namely, it is 

 useless at night, and yet ships sail as much then as in 

 the day. The value of this mode of correspondence is 

 thus reduced one-half, and an owner wishing to give 

 final instructions to his captain by this means, hesitates 

 in doing so, as he is not certain that his ship may pass 

 the lighthouse in the day. 



La Cour's system is not intended to supersede the 

 present flag system, but to supplement it in the night. 

 This invention enables us to utilise a corresponding 

 modus operandi at night by means of the same signal- 



book, and in such a way that the night duty becomes as 

 simple as the day duty, and even possesses certain ad- 

 vantages over the latter. 



When we observe a distant white light, a star, or the 

 light from a lighthouse through a prism with vertical 

 edge, then such a light, as is well known, appears as a 

 horizontal luminous line, consisting of red, orange, 

 yellow, green, blue, indigo, and violet-coloured rays. Sir 

 Isaac Newton discovered that this was owing to the fact 

 that the white light in reality is a combination of all 

 these colours, with their infinitely many shades, and 

 that they are refracted differently in the prism and thus 

 separated, whilst they can again be combined and repro- 

 duce the white light. 



Instead of a simple, a compound prism may be used. 

 The latter separates the colour rays, but does not, on 

 the whole, deflect them much from their originaldirection, 

 and such a prism fixed on a telescope (fig. 1) is specially 

 adapted to dissolve the in-going light. When a distant 

 white spot of light is observed through this, a luminous 

 line (fig. 2) is seen in the field of the- telsecope, coloured 

 from red to violet. 



If now the person who is sending the light signal is 

 able to arrange, in a simple manner, that all the 



F13. 4. 



colour rays are not emitted, but only some, while others 

 are entirely removed, it can be so managed that the 

 remaining part of the spectrum appears as a distinct 



signal, for instance the Morse signal - - (fig. 3.) 



This is exceedingly easy to decipher, and does not even 

 require colour sense, for although it is differently 

 coloured, yet it is only the shape which is of importance 

 (the colours are the only means of providing the conven- 

 tional shape), and the signal can be read by any one, 

 even the colour blind. 



The sending instrument is represented diagramati- 

 cally in fig. 4, which shows a horizontal section of the 

 instrument (it is about 1 foot high and long, and 8 inches 

 wide), together with the rays of light on their road to 

 the horizon. F is the lamp, S, K is -the screen, in which 

 openings are cut corresponding to the signals to be sent, 

 for instance, two small openings (1 and 2) and one wide 



(3), corresponding to the signal . L is a lens, 



the distance of which from S, K is equal to its focal 

 length. Therefore all the rays of light which, passing 

 through the opening I, strike the lens L, will, after travel- 

 ling through it, become parallel with the line, 1— o, from 

 the opening, 1, to the optical centre of the lens (o). The 

 other rays of light are therefore not shown, for they 

 have the same direction as 1 — o. This ray of light will 

 then strike the prism P, and be refracted and spread, so 

 that it forms the coloured, fan-shaped rays of light i\, v„ 



