176 



POPULAR SCIENCE I!TEWS. 



[December, 1SS9. 



blaze of light, as the well-known drawing of 

 Lord Rosse (which, however, lays no claim 

 to minute accuracy) ; but on the little photo- 

 graph every real wisp of nebula appears in 

 its true place, and there are numerous 

 "knots," not shown in the old drawing, 

 where the nebulous matter seems to be gath- 

 ering into globes, besides many streams of 

 minute stars which stand in evident relation 

 to neighboring filaments of the nebula. 

 These stellar streams form a marked feature 

 in nearly all the photographs of the more 

 brilliant nebulae. They appear to be formed 

 by the collection of the nebulous matter into 

 isolated masses that are denser and more 

 luminous than the rest. Whether this view 

 is correct or not, the star-streams are certainly 

 significant. 



Mr. Huggins' recent photographs of the 

 spectrum of the nebula of Orion indicate the 

 same thing in a diflerent way. In one of his 



lines, when first discovered, was, for a time, 

 attributed to nitrogen ; but it soon appeared 

 that this identification is untenable. The 

 principal lines of hydrogen are unquestionably 

 present, but this bright green line, which is 

 far more conspicuous than any of the others, 

 has thus far remained a mystery. Very 

 recently, Mr. Lockyer, in connection with 

 his "meteoric hypothesis," (in which he 

 attempts to explain most of the phenomena 

 of the heavenly bodies by the assumption that 

 they are all mere swarms of such meteoric 

 stones as fall upon the earth now and then), 

 has maintained that this line in the spectrum 

 of the nebula is simply the remnant of one of 

 the bands in the spectrum of magnesium — a 

 metal which is commonly found in aerolites. 

 The elaborate investigation of Dr. and Mrs. 

 Huggins, who worked together in the obser- 

 vations, is conclusive in proving that this is 

 an error ; the mvsterv remains unsolved. 



observations the slit of the instrument was so \ 

 adjusted that the image of one of the stars of j 

 the "trapezium" fell upon it. As a result,' 

 the spectrum, as photographed, shows several 

 groups of bright lines, which cross the star- 

 spectrum and extend out into the nebula- 

 spectrum on each side. This is just what 

 should happen if these "stars" in the nebula 

 are balls of the nebulous matter condensed to 

 a certain degree, but not quite to the state of 

 ordinary stars, which show no bright lines in 

 their spectrum. 



As our readers doubtless remember, Mr. 

 Huggins was the first to observe visually 

 the spectrum of a nebula (in 1864), and 

 the first to get a photographic impression 

 of such a spectrum (in 1881.) His latest 

 observations have been visual as well as 

 photographic, and have been made specially 

 to test Mr. Lockyer's attempted explanation 

 of the origin of the principal bright lines in 

 the nebula-spectrum. The brightest of these 



We must not close our sketch of recent 

 progress without referring to Professor Hol- 

 den's telescopic observations at the Lick 

 Observatory. In the case of the numerous 

 nebulse which are not, like the inajority, mere 

 oval balls of shining cloud, but are irregular 

 in form, and composed of luminous filaments 

 surrounded by an envelope of fainter light, he 

 finds that the apparent shape of the filament 

 which forms the core of the structure can be 

 explained by supposing it to be in reality a 

 sort of "helicoid," or cork-screw spiral, seen 

 under a special angle. A wire bent into such 

 a helicoid, and looked at from diflerent points 

 of view, presents a great variety of outlines, 

 which very accurately represent the otherwise 

 inexplicable forms of these irregular nebula". 



As is obvious from what has been said, the 

 main conclusions which had been arrived at 

 sixteen vears ago are all confirmed. It is 

 clearer than ever that the nebijla; are not 

 "distant galaxies" far beyond the stars. 



They are not clusters of full-sized stars, 

 which appear nebulous only because of their 

 inconceivable remoteness, but they are clouds^ 

 and their luminosity is due to shining gases, 

 among which hydrogen is present, though the 

 gas which furnishes the brightest light re- 

 mains still unknown. Moreover, these clouds, 

 whatever else they iriay contain besides the 

 luminous gases, are somehow kindred to the 

 stars, and associated with them in such a way 

 as to suggest almost irresistibly that the neb 

 ula is the material out of which stars are 

 made. 



The question of their permanence remains 

 unsettled. It is altogether probable that pro- 

 cesses are going on within them which slowly 

 alter their conditions, but time alone can 

 determine the rate and nature of such 

 changes ; the evidence, as yet, is indecisive. 



Princeton, N. J., Oct. 31, 1889. 



A MONSTER KALEIDOSCOPE. 



One of the novelties exhibited at the Paris 

 Exposition was an arrangement of three large 

 mirrors placed so as to form an equilateral 

 triangle, with sufficient room in the centre for 

 several ]3ersons to stand. It was, in fact, a 

 great kaleidoscope, in which living men and 

 women took the place of the bits of colored 

 glass with which tlie well-known optical toy 

 is provided. 



13y a law of optics, the image of any object 

 placed in the centre of the space enclosed hy 

 the mirrors will be produced an indefinite 

 number of times in groups of six, symmetri- 

 cally distributed through the field of view 

 given by the mirrors. The number of reflec- 

 tions is theoretically infinite, but the images 

 rapidly become dim and indistinct, through 

 repeated reflections, and fade away in the 

 apparent distance. 



The illustration (from La Nature^ shows 

 the eflect produced by a group of three per- 

 sons occupying the space enclosed by the 

 mirrors. Two of the mirrors are shown, but 

 the third one — which should be in front — is 

 necessarily omitted in the engraving. The 

 three individuals see themselves transformed 

 into an immense crowd, arranged in regular 

 lines, and apparently awaiting the passing of 

 a procession. By waving their hats, the 

 crowd becomes wildly enthusiastic, and the 

 three quiet and respectable persons have only 

 to walk back and forth for a step or two to 

 produce the appearance of an immense mob, 

 rushing about in the greatest excitement and 

 confusion, and ready for any mischie' jr vio- 

 lence that may come in its way. 



This illusion is a most ingenious adaptation 

 of a familiar principle in optics, and must be 

 very puzzling to those who are unacquainted 

 with the laws governing the reflection of light. 

 The same eflect can be produced with mirrors 

 of ordinary size, by substituting dolls or any 

 small object for living persons. By varying 



