172 



NA TURE 



[Dec. 28, 1 87 1 



The vertebral blocks, as well as the ribs, are the product of 

 the primitive axial series of (invertebral) discs, vi'hich, when 

 completely arrayed, each bear five branches, viz., two pair of 

 haemal arches, two pair of neural arches, and a fascicle of parallel 

 elects, so to spealc, which being cemented together, both in the 

 front and rear, l^y the superficial ossification of the discs at either 

 end, are fuied into the bloclt piece-;, as found, eg. in the young 

 hog ; the cementing slab covering the big neural rib head like- 

 wise, and not only the pentagonal prismatic block. The first 

 disciform ossification we find in the corals, forming cribrose 

 ethmoidal discs, such as the closely set " sigillate impressions" 

 of tlie Astraja, and afterwards left behind as the coccyx, e.g., of 

 Byathophyllum. 



SIEMENS' DYNAMO-ELECTRIC LIGHT* 

 J\ SERIES of experiments was made last week at Sheerness, 

 with a view of ascertaining the applicability of Siemens' 

 dynamo-electric light to torpedo services in time of war. This 

 scientific combination is produced, as its name signifies, by the 

 application of excessively rapid motion generated from the fly- 

 wheel of a steam-engine to a very powerful set of ordinary gal- 

 vanic " coils " in connection with soft-iron magnets. The leather 

 strap from a four-horse power engine, encircling a small gun 

 metal pinion, causes it to revolve with the extreme velocity of 

 1,600 revolutions per minute, inducing motion in an electric 

 ''bobbin " at the side of an apparatus consisting of several sets 

 of strong insulated coils. A stream of electricity consequently 

 passes through them. This stream is conducted to a second series 

 of coils, larger and more powerful than the first, which are also 

 in combination with a pinion revolving 800 times per minute, 

 thus intensifying the stream as it passes through them to a very 

 considerable degree. Both negative and positive currents are 

 now alternately given off from another "bobbin " at the side of 

 the second series of magnetic coils, to the train of insulated wires, 

 which conveys them to the position from which the dynamo- 

 electric light is to be exhibited. Here there is a delicately con- 

 trived apparatus for containing the carbon points, between whicli 

 the light is to be generated, adjusted at the top of a tripod some- 

 what similar in construciion to that of a surveying instrument. 

 At the back of the two carbon points, and " si jtted " vertically 

 to admit of their holders passing through it, is a concave reflectijr 

 of white polished metal, which collects the rays of light into a 

 focus, and transmits them in any required direction by means (:*f 

 an adjusting hand wheel below. A minute aperture in the centre 

 of the leflector, precisely behind the junction of the two carbon 

 points, throws a representation of the flame upon a piece of opal 

 gla^sin a frame fixed at the back of the reflector ; and through the 

 agency of another small hand wheel which causes the carbon 

 points to approach or recede from each other, the flame can 

 be reduced or intensified at pleasure, by simply turning the 

 wheel, care being taken at the same time to keep a watchful 

 eye upon the picture produced, as the withdrawing of the 

 points to too great a distance from each other will extinguish the 

 light. It should have been remarked before that ample means 

 are taken by lubricating the electrical apparatus to counteract 

 the evil efTects which might otherwise arise from the excessive 

 friction consequent on the rapidity of motion in the several parts. 

 Tne object of instituting the series of experiments which were 

 made on Monday was to ascertain if it was possible to throw 

 such a stream of light upon an enemy's working parties engaged 

 in interrupting communications with a line of torpedoes at night, 

 as would render them sufficiently conspicuous to be fired at and 

 consequently driven off. The place selected was the new fort at 

 Garrison Point, Sheerness. The engine and "coils" were 

 erected in the enclosure of the fort, while the instrument itself 

 was placed in one of the massive embrasures piercing its sides. 

 No sooner was steam got up and the order given to turn ahead, 

 than the burring noise of the machine indicated that electricity 

 was being rapidly generated, sparks and stars of vivid blue light 

 being given off at the various joints. Another instant, and a 

 vivid stream of light shot across the sea to a number of ships 

 lying in the offing at a distance of about two miles, lighting them 

 up with the brilliancy and distinctness of broad moonlight. The 

 effect was magnificent. Clouds of mists, rendered visible by the 

 intensity of the rays shooting through them, rolled across the 

 broad field of bright light from time to time, not, however, in- 

 terrupting the view in their progress. By shifting the direction 

 of the rays laterally, each object in turn came within the compass 

 * Reprinted from the Times. 



of the portion of horizon rendered clear. In fact, it was 

 sufficiently apparent that no objects of any appreciable size, 

 such for instance as an enemy's boats, could come within a mile 

 or more of one of Siemen's dynamo-electric instruments in opera- 

 tion without being rendered conspicuous to any battery in the 

 vicinity, and consequently involving to themselves the most 

 imminent danger. Hence the result of the experiments may be 

 pronounced a success ; whether, however, a corresponding effect 

 might not be obtained by a succession of parachute lights thrown 

 from a rocket or mortar is quite an open question. 



PHYSICS 

 Note on the Spectrum of the Aurora 



On the evening of November g there appeared one of the 

 most magnificent crimson auroras ever seen at this place. 

 When first observed, at about a quarter before six P.M., it con- 

 sisted of a brilliant streamer shooting up from the north-western 

 horizon ; this was continued in a brilliant red, but rather nebu- 

 lous mass of light, passing upward and to the north. Its highest 

 points were from 30° to 40' in altitude. A white aurora, con- 

 sisting of bright streamers, appeared simultaneously, and extended 

 round to the north-east.* 



The crimson aurora was examined with the spectroscope at 

 six o'clock. The instrument used was a single glass-prism spec- 

 troscope, made by Duboscq, of Paris. On directing the slit 

 toward the brilliant streamer above mentioned, a bright spectrum 

 was observed consisting of five well-marked lines. A millimetre 

 scale attached to the instrument was then illuminated with a gas 

 flaine, the auroral lines being readily measured, even when the 

 numbers on the scale were bright enough to be read distinctly. 

 The sodium line was used to adjust the scale, being equally 

 divided by the division 100 ; the width of the slit was about one 

 millimetre. As thus arranged, the five auroral lines, beginning 

 at the red end, had the following positions: — Scale-Nos. 90, 

 liO'5, 130, 138, 149. The brightness of the lines was, following 

 the above order, 3, I, 5, 2, 4, the second line from the red end 

 of the spectrum being the brightest. The line marked 90 and 

 the one marked ilO'5 were sharp and well defined ; the others 

 were all nebulous on the edges. Before the measureinents were 

 completely verified by a second comparison, the crimson aurora 

 entirely vanished, having endured less than half an hour. In the 

 white aurora which reinained, the speclroscop; showed four of 

 the five lines given ; the crimson line alone was absent. The 

 measurements are exact to half a division of the scale. 



To determine the approximate wave-lengths of these lines, 

 comparison was made both with certain metallic lines and with 

 the lines of the solar spectrum. On the scale of this instrument 

 the metallic lines employed read as follows: — 

 Ka 63, Lia 79, Sr;3 8o, H(f) 82, Caa 91, Sra 96, Cafl 113, H(/) 



146-5, Sr8 163, Cs6 165, Csa 167, Rba, & 5 200, K;8 218. 

 The Fraunhofer lines measured as follows : — 



a 70-5, B 76, C 82, D 100, E 124-5, ''' 13°. F H^'S. G 189. 



Direct interpolation was used in comparing the wave-lengths of 

 the auroral lines with those given above, the wave-lengths of the 

 Fraunhofer and eleitiental lines being taken from Gibbs's tables 

 (Amer. Jour, of Science and Arts, II. xliii. i ; xlvii. 194). This 

 method was believed capable of giving results as close as the 

 instrumental measui-ements. Iir this way the wave-lengths of the 

 five auroral lines were obtained, as given in the following table : 



Scale Wave- Auroral 



Line. number. length. lines. Other measurements. 



B 76 6S7 



C 82 656 



(i) 90 623 623 627 Zollner. 



1) 100 5S9 



(2) IIO-5 562 562 557 Angstrbm. 

 E 124-5 5^7 



(3) 130 517 517 520 Winlock. 

 b 130 517 



(4) 138 502 502 

 F 146-5 4S6 



(5) 149 482 4S2 4S5 Alvan Clark, Jr. 

 G iSg 431 



* Professor Newton informs m: that he obsirved an equally briliiaat red 

 patch of aurOi-al light in the north-east, five or ten minutes earlier. Since the 

 lower end of the red streamers was much lower than that of the white, it 

 would seem as if the red were .seen through the white, the red beinij most 



