SCIENTIFIC SIDE-LIGHTS 



Space 

 Spectrum 



remains have been found in Sweden, in Ger- 

 many, in France as far as the Pyrenees, and 

 in Central Italy. It seems, however, to have 

 been most abundant in the British Isles, 

 and especially in Ireland. AVEBURY Pre- 

 historic Times, ch. 9, p. 278. (A., 1900.) 



3166. SPECIES, SUPPOSED, PROVED 

 TO BE VARIETIES A small butterfly 

 (Terias hecabe) ranges over the whole of 

 the Indian and Malayan regions to Austra- 

 lia, and everywhere exhibits great varia- 

 tions, many of which have been described 

 as distinct species ; but a gentleman in Aus- 

 tralia bred two of these distinct forms (T. 

 hecabe and T. JEsiope), with several inter- 

 mediates, from one batch of caterpillars 

 found feeding together on the same plant. 

 It is therefore very probable that a consid- 

 erable number of supposed distinct species 

 are only individual varieties. WALLACE 

 Darwinism, ch. 3, p. 31. (Hum.) 



3167. SPECTACLE OF ACTION 



STIMULATES ACTION Value of Competi- 

 tion. The deepest spring of action in us is 

 the sight of action in another. The spectacle 

 of effort is what awakens and sustains our 

 own effort. No runner running all alone 

 on a race-track will find in his own will the 

 power of stimulation which his rivalry 

 with others incites, when he feels them 

 at his heels, about to pass. When a trotting 

 horse is " speeded," a running horse must go 

 beside him to keep him to the pace. JAMES 

 Talks to Teachers, ch. 7, p. 53. (H. H. & 

 Co., 1900.) 



3168. SPECTROSCOPE HELPS 

 SOLVE MYSTERY OF AURORA Deter- 

 mines What It Is Not Its Light from Lumi- 

 nous Gases. If the light emanating from a 

 solid or liquid incandescent body be passed 

 through the spectroscope the resulting spec- 

 trum is continuous. If, on the contrary, 

 the source of light is gaseous, the spectrum 

 is composed of a certain number of bright 

 lines or stripes, separated from each other 

 by dark intervals. . . . 



The spectrum of the aurora borealis, stud- 

 ied for the first time by Angstroem in 1866, 

 is essentially a spectrum of lines; the light 

 of the aurora is the product, therefore, of 

 luminous gases, and not of solid or liquid 

 incandescent particles; neither can it be 

 due, as has sometimes been supposed, to a 

 reflection of the light of the sun. ANGOT 

 Aurora Borealis, ch. 3, p. 42. (A., 1897.) 



3169. SPECTRUM ANALYSIS Each 

 Metal Gives Its Own Unvarying Bands Dis- 

 tinction between Things Seemingly Identical. 

 Within the camera is now placed a cylin- 

 der of carbon hollowed out at the top to 

 receive a bit of metal; in the hollow is 

 placed a fragment of the metal thallium. 

 Down upon this we bring the upper carbon 

 point, and then separate the one from the 

 other. A stream of incandescent thallium 

 vapor passes between them, the magnified 

 image of which is now seen upon the screen. 



It is of a beautiful green color. What is 

 the meaning of that green? We answer the 

 question by subjecting the light to prismatic 

 analysis. Sent through the prism, its spec- 

 trum is seen to consist of a single refracted 

 band. Light of one degree of refrangibility, 

 and that corresponding to this particular 

 green, is emitted by the thallium vapor. 

 We will now remove the thallium and put 

 a bit of silver in its place. The arc of silver 

 is not to be distinguished from that of thal- 

 lium; it is not only green, but the same 

 shade of green. Are they then alike? Pris- 

 matic analysis enables us to answer the 

 question. However impossible it is to dis- 

 tinguish the one color from the other, it Is 

 equally impossible to confound the spectrum 

 of incandescent silver vapor with that of 

 thallium. In the case of silver, we have two 

 green bands instead of one. . . . We 

 have in these bands a perfectly unalterable 

 characteristic of the two metals. You never 

 get other bands than these two green ones 

 from the silver, never other than the single 

 green band from the thallium, never other 

 than the three green bands from the mixture 

 of both metals. Every known metal has its 

 own particular bands, and in no known 

 case are the bands of two different metals 

 alike in refrangibility. It follows, there- 

 fore, that these spectra may be made a sure 

 test for the presence or absence of any par- 

 ticular metal. If we pass from the metals 

 to their alloys, we find no confusion. Cop- 

 per gives green bands; zinc gives blue and 

 red bands; brass, an alloy of copper and 

 zinc, gives the bands of both metals, per- 

 fectly unaltered in position or character. 

 TYNDALL Lectures on Light, lect. 6, p. 193. 

 (A., 1898.) 



3170. 



Gases Tell Their 



Story Far-off Nebulce Analyzed. If a solid 

 or a liquid is heated to such an extent 

 that it becomes incandescent, the spectrum 

 which its light gives is, like the rain- 

 bow, a broad colored band without any 

 breaks, with the well-known series of col- 

 ors red, yellow, green, blue, and violet, 

 and in no wise characteristic of the nature 

 of the body which emits the light. 



The case is different if the light is emit- 

 ted by an ignited gas or by an ignited 

 vapor; that is, a substance vaporized by 

 heat. The spectrum of such a body consists, 

 then, of one or more, and sometimes even a 

 great number, of entirely distinct bright 

 lines, whose position and arrangement in 

 the spectrum are characteristic for the sub- 

 stances of which the gas or vapor consists, 

 so that it can be ascertained, by means of 

 spectrum analysis, what is the chemical 

 constitution of the ignited gaseous body. 

 Gaseous spectra of this kind are shown in 

 the heavenly space by many nebulae; for 

 the most part they are spectra which show 

 the bright line of ignited hydrogen and oxy- 

 gen, and along with it a line which, as yet, 

 has never been again found in the spectrum 



