]64 



♦ KNOWLKDGE ♦ 



[June 1, 1889. 



In South America, Brazil has long been famous for its 

 gold mines ; but gold is also found in the Argentine 

 Republic, Venezuela, Colombia, and Guiana. 



Australia is famous for its gold, and all who visited the 

 Indian and Colonial Exhibition will remember the great 

 arches buOt to represent the output from Victoria and New 

 South Wales. It is also found in tjuaensland. South 

 Australia, New Zealand, &c. 



THE SPECTRUM OF THE ORION NEBULA. 



R. HUGGINS has kindly sent us an early 

 copy of an important paper he has com- 

 municated to the Royal Hor-iety on the 

 spectrum of the above nebula, with a copy 

 of a photograph showing some twenty -five 

 very sharply-defined lines in its spectrum, 

 and in the spectrum of the stars of the 

 trapezium. At least four groups of bright lines in the 

 spectrum of these stars can be traced into the nebula 

 for some little distance from the stars. Dr. Huggins 

 says : — 



" It is scarcely necessary to state the importance of this 

 observation as showing that these stars of the trapezium 

 are not merely optically connected with the nebula, but are 

 physically bound up with it, and are very probably con- 

 densed out of the gaseous matter of the nebula. . . . 

 The first group of six lines occurs between \ 4116 and 

 4167. The lines of this group do not extend far from the 

 continuous star spectra, with the exception of two lines. 

 These can be seen faintly in another photograph taken in 

 1889. Beyond there is a fainter group, probably of four 

 lines a little beyond h. I am pretty sure that these lines 

 extend into the nebula. The third group from X .3896 to 

 3825, of which I have endeavoured to measure ten lines, 

 is faint ; but there is no doubt that the same lines are 

 present in the adjoining nebular matter. There are two 

 lines a little more refrangible than the strong line seen in 

 1882, at about X 3709 and X 3699. 1 have a suspicion of a 

 faint group about this place, and also of another group on 

 the less refrangible side of G." 



Dr. Huggins stated in 1872, as the result of numerous 

 direct comparisons of the brightest of the nebula lines with 

 the brightest line in the spectrum of nitrogen, that the 

 nebula line was " sensibly coincident with the middle of 

 the less refrangible line of the double line of nitrogen." 



In a still more critical examination of the position of the 

 nebula line for the purpose of determining whether there 

 was any indication of relative motions of the gaseous 

 nebulas in the line of sight, he found some experimental 

 difficulty from the circumstance that the nebula line is 

 narrow and defined while N, is nebulous, but he was 

 fortunate in finding a more suitable fiducial line of com- 

 parison in a narrow line of lead which falls almost upon 

 the middle of N,. In December, 1872, he compared this 

 line directly with N,, and found it sufficiently near in 

 position to serve as a fiducial line of comparison. 



Six other gaseous nebulse were also examined, each on 

 several nights, with the result that " in no instance was any 

 change of relative position of the nebula line and the lead 

 line detected." 



In the simultaneous observation of the nebula line and 

 the lead line it was found that if the lead line was made 

 rather less bright than the line of the nebula, the small 

 excess of apparent breadth of this latter line appe<ared to 

 overlap the lead line to a very small amount on its less 

 refrangible side, so that the more refrangible sides of the 

 two lines appeared to be in a straight line across the 



spectrum. The closeness of position of the two lines was 

 shown by the observation that when the line of the nebula 

 passed across the field of the spectroscope, and the lead line 

 was thrown in, nothing was seen but an increase in bright- 

 ness of the nebula line. By comparing the end of the 

 nebula line near the trapezium, where it is refined to a 

 point, he estimated that the difference of position of the 

 middle of the lead line and that of the nebula line might 

 be ' possibly from ,\ 0000-2 to A. 0000-3. Some recent 

 measures of the position of the lead line with the middle 

 of N, show that the lead line is about X 0000-12 more 

 refrangible. 



These direct comparisons of the nebula lino with the 

 lead line confirmed his former conclusion, that the brightest 

 line in the gaseous nebula; is very near N,, when seen under 

 a dispersion equal to nearly eight prisms of 60, namely, 

 36° 25' from A to H. 



Dr. Huggins's final determination of the wave-length of 

 the brighte;-t nebula line is X 500-1 6 to X 50048. 



In a paper read before the Royal Society in 1887, Mr. 

 Lockyer says : — " Only seven lines in all have been 

 recorded up to the present in the spectra of nebuL-p, 

 three of which coincide with lines in the spectrum of 

 hydrogen and three correspond to lines in magnesium. 

 The magnesium lines represented are the ultra-violet low- 

 temperature lines at 373, the line at 470, and the remnant 

 of the magnesium fluting at 500, the brightest part of the 

 spectrum at the temperature of the Bunsen burner." 



As Mr. Lockyer's theory, that the nebula^ are composed 

 of sparse meteorites, the collisions of which bring about a 

 rise of temperature sufficient to render luminous one of their 

 chief constituents, magnesium, is based upon the .ibove 

 statement that the nebula lines correspond with the mag- 

 nesium fluting. Dr. Huggins thought it de.sirable, on 

 account of the " grave theoretical conclusions which Mr. 

 Lockyer had based on his statement of their coincidence and 

 on that of the photographic line about 3730 with the next 

 strongest group of the burning magnesium spectrum, to 

 undertake the laborious task of comparing, with the neces- 

 sary care and precautions, the nebula line directly, in the 

 spectroscope attached to the telescope, with the spectrum of 

 burning magnesium. 



Dr. Huggins says : " It will be seen by a reference to 

 Mr. Lockyer's statement that he escaped from the difficulty 

 of the known difference in position of the nebula line and 

 that of the magnesium- flame band, by having taken the 

 wave-lengths to three figures only." 



Arrangements were made by which the light from 

 burning magnesium was thrown into the telescope from the 

 side and then reflected down, under conditions similar with 

 the light from the nebula, upon the slit of the spectroscope. 

 By this arrangement any flexure in the tube connecting the 

 spectroscope with the telescope W'ould affect both spectra 

 alike. The direct comparison was successfully made on 

 ISIarch 6. But Dr. Huggins failed to find the coincidence 

 in position asserted, and the nebula lines are sharp, and 

 show no winged character corresponding with the flutings 

 of the magnesian spectrum. 



The positions of the lines observed and photographed in 

 the spectrum of the nebula are : — 



Line measured by Dr. Copeland, probablj- D., . X.5874-() 



Brightest line .50011; lo ."lOOl-S 



Second line ....... 4it.570 



Third line, H0 -ISeo-T 



Fourth line, H7 4310 1 



Line measured by Dr. Copeland . . . 4476-0 

 Strong line in photographs 1882 and 188S about H724 

 Line in photographs 1888 . . . . „ 37090 



36990 



Photograph 1889. 1st pair . J " 3741-0 



