58 



SCIENTIFIC NEWS. 



[July 20, I J 



containing all the colours. In the direction of the distant 

 observer, i, a distinct colour only will be emitted from 

 the opening 1, say orange; from the opening 2, there will 

 also be rays emitted, which are first made parallel by the 

 lens, and afterwards spread by the prism in the fan- 

 shape r s> v,, of which a single colour only strikes 2', say 

 yellow. In the same way the opening, 3, produces the 

 fan-shape r 3 , v v but this opening being wider, i will re- 

 ceive several kinds of green and blue rays. 



To the naked eye, or with an ordinary telescope, the 

 light which issues in the direction i, will give shapes of 

 colourcorresponding to a mixture of the respective colours; 

 but if the spectro-telegraphic telescope is used, the sig- 

 nal appears as in fig. 3. 



When the sender moves the screen S, K, in the direc- 

 tion indicated by the arrow, opening 3 will take opening 

 2's place, opening 2 takes i's place, and in the field of 

 the telescope the receiver will also see the line of light 

 3, slide smoothly into 2's place, etc., etc., so that the sig- 

 nals are seen to glide through the field, in at one side 

 and out at the other. 



To perfect the present system of signalling, and use 

 La Cour's signals at night, a sending instrument, with the 

 eighteen perforated metal pieces, together with the 

 receiving telescope is only required. Instead of hoisting 

 the four flags in the daytime, signifying, for instance, 

 C, F, G, L, the four corresponding pieces of metal need 

 only be inserted in the sending lantern, and made to 

 move backwards and forwards several times,- so that the 

 receiver has time to read them. 



These night signals are in some respects superior to 

 the day signals. They are, for example, not diminished 

 by distance, as their size only depends upon the receiv- 

 ing telescope, so that however far they are sent they 

 keep the same dimensions. They are also independent 

 of the direction of the wind, which often disturbs the flag 

 signals by making them turn edgeways to the observer 

 so that he cannot see them. 



This same system has been tried for ordinary tele- 

 graphy by passing a perforated slip (as in the Wheat- 

 stone's transmitter) through the sending instrument, and 

 a telegraphist can read these marks so easily, that the 

 telegraphing can be performed with the same speed as 

 with an ordinary Morse instrument. 



It is well known that a hazy atmosphere first obli- 

 terates the violet and blue rays of light ; it has there- 

 fore been supposed by some that spectro-telegraphy 

 would fail under these circumstances. This is, however, 

 not so, for as the signals seem to glide through the whole 

 sp:ctrum, they can always be read in the red, 

 yellow, and green, even if they are lost in the violet 

 and blue. 



This principle also appears to be applicable in several 

 different ways. If a lighthouse be supplied with a 

 sending instrument, in which the first letter or letters 

 of the light's name are placed, the mariner will always 

 be able to see in the spectro-telegraphic telescope what 

 light it is, and thus mistakes and loss may often be pre- 

 vented. 



Further, an entrance to a harbour does not need to 

 be indicated by two lights, which direct the course, but 

 by one only of La Cour's system, with a fixed signal or 

 letter, which is only seen in the middle of one's tele- 

 scjpe, if one is exactly on the right track. By steering 

 a little to the one side or the other, the letter cr signal 

 will appear to glide in the telescope to either of the two 

 sides and if ths Uiip parses entirely out of the proper 



course the signal disappears from the field of the tele- 

 scope. Another advantage in this method is, that the 

 light from the harbour lantern is very easily distin- 

 guished from all other lights, for these latter appear in 

 the telescope as a continuous light from red to violet, 

 whereas the former gives its own peculiar signal, for 



example . 



Finally, ships might be supplied with a fixed lantern 

 of this kind, which throws light forward, and obliquely 

 to the sides. Two ships going in opposite directions 

 will thus in their telescopes immediately see whether 

 their course lies to the starboard or port of each other, 

 and also whether they are in the act of altering their 

 helms, for the letters in the telescope will then appear 

 to glide to one side or the other. — Electrical Review. 



The Elastic Limit of Iron and Steel. — An interesting 

 series of experiments on the alteration of the elastic limit of 

 iron and steel, which have now extended over several years, 

 have been made by Professor Bauschinger at the laboratory 

 of the Technical High School at Munich, and some very in- 

 teresting and important results have been obtained. Most of 

 the experiments were made on one of Werder's testing 

 machines, the deformation being read by Professor Bau- 

 schinger's mirror apparatus, but for the experiments on the 

 endurance of bars a Woehler machine has been employed. 

 In the course of these experiments it was discovered that the 

 break-down point of a bar had no connection with the elastic 

 limit : thus, when a series of gradually-increasing stresses, 

 exceeding that corresponding to the original break-down 

 point of the material were applied to the bar, this point rose 

 with the stress, and this rise was continued for weeks and 

 months, and possibly years, if the bar was left at rest under 

 the greatest of these loads. On the other hand, when a bar 

 was subjected to an increasing stress, greater than that cor- 

 responding to the elastic limit of the material, but less than 

 the stress at the breaking-down point, the elastic limit and 

 elastic modulus both increased, but reached a maximum as 

 the breaking-down point was approached, and then rapidly 

 decreased, the former at times even reaching the value of 

 zero. If, however, the bar is left at rest under a stress ex- 

 ceeding that of the primitive breaking-down point, the elastic 

 limit and elastic modulus increase again, and the former may 

 attain a point far above its original value. Moreover, the 

 limit in elastic tension is, in general, very different from that 

 of the material when subjected to compression, and artificially 

 raising the elastic limit in tension, as described above, causes 

 the limit in compression to be decreased, and this may even 

 pass through the point of zero stress. In other words, a bar 

 of steel or iron has two elastic limits, and whatever position 

 these occupy on the scale of loads, the range between them is 

 nearly a constant quantity. By alternately stressing a bar 

 in tension and compression just beyond the elastic limits, 

 these, after a certain number of repetitions, occupied posi- 

 tions equally distinct from the point of zero load, and the 

 limits thus obtained are called by Bauschinger the natural 

 elastic limits of the bar. It was then noted that the stress 

 corresponding to these limits sensibly coincided with that 

 found by Woehler as the limiting stress to which a bar could 

 be subjected to alternate tension and compression. It would 

 thus appear thatabar would bear an indefinite number ofrepe- 

 titions of stress, provided the range of stress does not exceed 

 the elastic range mentioned above. — Glasgow Engineer. 



Hawick Scientific and Philosophical Society.— At 

 the annual general meeting the following gentlemen were 

 elected officers and council of the society :— President, Mr. 

 John Berry, Stewartfield ; Vice-President, Mr. James Gowans, 

 jun. , extra Vice-Presidents, Mr. W. S. Irving and Mr. John 

 N. Lamb; Secretary, Mr. JohnN. Lamb ; Assistant Secretary, 

 Mr. David Miles ; Treasurer, Mr. W. C. Goodfellow; Council, 

 Messrs. A. Blackwood, A. Huggan, W. S. Irving, W. Sinclair, 

 R. Watson, and Jas. Young. 



