28 



SCIENTIFIC NEWS. 



[Jan. 13, iS 



^nd the other end movable by means of a lever (not 

 shown). Dividing screens (T) also pass along the eye- 

 piece tubes, coming quite up to the lenses. A round piece 

 of ground glass (K) is held in its position by means of a 

 screw (L), for use when other than sunlight is looked at. 

 The whole instrument is placed on a stand, where an ar- 

 rangement is made for elevating the front end, to allow 

 of direct skylight being used. 



The horizontal movable screen forms an important 

 part. When it is raised the coloured lights fall on the 

 eye-pieces ; and when it is lowered the coloured lights 

 are cut off, the white light from the upper opening en- 

 tering the lenses. When the screen is horizontal, and 

 the coloured sectors are properly adjusted, a perfect match 

 can be made, so as to observe a white disc with a black 

 bar across the middle, the upperhalf being the pure white 

 skylight through the clear glass, and the lower half being the 

 mixed white light through the regulated coloured glasses. 

 The instrument will combine any colours and show the 

 result of the combination, and any proportions of each 

 colour can be determined by the help of the shutters. It 

 is found that there is an infinite variety of colours which 

 vv^hen combined in proper proportions will give white. 

 It is also proved that with red (R), green (G), and violet 

 (V), in the sectors and proportioned by the shutters, all 

 possible colours with their shades and tints can be pro- 

 duced. But by no combination of colours (other than 

 red, green, and violet) can these three colours be produced. 

 These, then, are the primary colours. What would Sir 

 Isaac Newton have thought if he had looked through this 

 instrument, seeing that he considered — half superstitiously 

 — that the seven colours of the rainbow were the primi- 

 tive colours ? 



In selecting the colours for the circular opening in the 

 bos, the best red is a ruby red glass, dark enough to give 

 only a band in the red when examined with the spectro- 

 scope : for green, a glass which passes a narrow band of 

 light in the green of the spectrum, and is about what is 

 known as emerald green ; and for violet a glass which 

 passes only the light of the violet end of thespectrum. When 

 the three colours are combined in the proper proportions, 

 so perfect a white can be produced with this chromomictor 

 that it is impossible to distinguish between the standard 

 white and the white produced by the three brilliant 

 colours. To get the perfect match of the two whites, 

 the surface of the interior of the box must be dead white ; 

 for any polished surface reflection would vitiate the effects. 

 The sun must not shine on the instrument, a bright sky 

 being most suitable. If the red and green shutters 

 be opened and the violet closed, the colour produced is a 

 canary-yellow of considerable brightness and strength. 

 {To be continued.) 



-"-JiWiSi^Sit-i 



FIRE FROM NITRIC ACID. 



'T'HERE was recently a prosecution before one of the 

 Prussian courts for danger caused to a train of rail- 

 way cars. The main question was whether fuming nitric 

 acid could occasion spontaneous ignition — which, after 

 hearing the sworn testimony of the court's expert 

 chemist, Dr. Jeserich, was decided in the affirmative. 

 The agent had sent by railway ten kilos (22 lb.) of fuming 

 nitric acid, the acid being contained in a strong stone 

 jar, tightly closed by a stone stopper and cement. The 

 whole was packed in straw within a wooden case. As, 



however, such dangerous liquids would not be carried by 

 rail as express freight, the contents of the box were re- 

 presented to be clothing, and by this irems the con- 

 cealed acid was sent by a passenger train. During the 

 journey the car containing the express freight was dis- 

 covered to be on fire. 



Before the flames had'made serious progress, the car was 

 uncoupled and shunted, the fire extinguished with slight 

 damage, and no person was injured. Examination 

 showed that the jar had leaked, and the acid had come 

 in contact with a roll of woollen cloth, whereby the 

 latter was set on fire. Dr. Jeserich gave it as his 

 opinion that all woollen goods, and all hair of animals, 

 horn, etc., have the property of igniting spontane- 

 ously when in contact with fuming nitric acid ; and he 

 stated that all the explosives, about which there has 

 been so much said and written lately, such as roburitej 

 melanite, etc., depend upon the action of nitric acid on 

 hair and wool. — All. Vers. Prcsse, Berlin. 



THE MECHANISM OF THE FLIGHT 



OF BIRDS. 



■yxrE shall here lay before our readers a brief summary of 

 the researches of M. Marey, condensed from the 

 pages oiLa Nature. The author has studied this subject by 

 the aid of "instantaneous " photography. The so-called 

 photographic revolver is capable of taking ten images of 

 a moving body per second. Thus the different postures 

 of a galloping horse or a flying bird can be accurately 

 represented, and points can be observed which utterly 

 escape the human eye. From a comparison of the dif- 

 ferent species of birds which have come under the 

 observatiop of M. Marey, he concludes that all execute 

 movements of the same nature In all the wing 

 closes in the act of being raised ; on arriving at the 

 highest point of its track, it is suddenly unfolded, and is 

 then depressed, moving forwards, and coming nearer the 

 body. At the end of this downward stroke the joints of 

 the wings fold up again, and the up-stroke re-com- 

 mences. Figure i shows the flight of the crested 

 heron (Ardea alba) moving transversely. Figure 2 repre- 

 sents the descending flight of the pehcan. 



These figures show curious attitudes which the eye 

 has not the time to seize, and with which we have not 

 been rendered familiar by the artistic representations of 

 birds. As it has been justly remarked by M. Maybridge, 

 European artists almost invariably represent flying birds 

 with their wings upraised ; the Chinese and Japanese, 

 on the other hand, represent them indifferently with 

 wings elevated or depressed. This does not imply that 

 the artists of the Far East have faithfully reproduced the 

 different attitudes of birds. A comparison of their draw- 

 ings with those obtained by instantaneous photography 

 shows that the human eye in China, no more than with 

 us, is able to seize actions which are merely momentary. 



The representations of a flying bird, if seen from a 

 single point of view, do not give us complete information 

 as to the nature of the movements of the wings. It is 

 necessary to photograph the bird under different aspects 

 to comprehend this mechanism. M. Marey has therefore 

 photographed flying birds from above, when passing 

 horizontally across the field of vision, and when moving 

 in a line towards the object-glass. These images 

 mutually complement each other. Birds seen from above 



