1887.] 



Researches on the Spectra of Meteorites. 



123 



many observers, down even to M. Cornn not so very long ago, have 

 been inclined to attribute it to the existence of "impurities." 



I began to map the so-called structural spectrum at the College of 

 Chemistry in 1869, but other matters supervened which prevented 

 the accomplishment of this work. This, however, is a matter of 

 small importance, because quite recently Dr. Hasselberg has com- 

 municated to the St. Petersburg Academy an admirable memoir on 

 the subject, accompanied by a map (' Memoires de l'Academie Impe- 

 riale,' Series vii, vol. 30, No. 7, Hasselberg). The brightest portions 

 of the structure- spectrum are shown in Map 2. 



The most convenient way of obtaining a supply of hydrogen for 

 investigations of this kind is to use a little sodium which has never 

 been in contact with hydrocarbon, or a piece of magnesium wire ; to 

 place them in the low end of a glass tube, one part of which can be 

 used as an end-on tube, and then, after ' getting a vacuum so perfect 

 that the spark will not pass, to slightly heat the metal. After a time 

 the spectrum of hydrogen, sometimes accompanied by the low-tem- 

 perature flutings of carbon, begins to be visible alike from the sodium 

 and the magnesium. 



If the vacuum has been very perfect to start with, at first the 

 bright lines C and F will be visible without any trace of structure, 

 and the hydrogen will be of a magnificent red colour. If now the 

 action of the pump be stopped, and the sodium be still more heated, 

 a point will be reached at which the conductibility of the gas is at its 

 maximum, and then, the jar not being in circuit, the structure- 

 spectrum of the gas will be seen absolutely alone, without any trace 

 of either C or F. The gradual disappearance of the F line is very 

 striking, and when the bright line is out of the field the lines due to 

 the structure seem to be enhanced in brilliancy. 



The brightest part of the spectrum is then that near D ; in the blue- 

 green we have a line at 464 more refrangible than F, and then a 

 double line at 4930 and 4935 ; other less refrangible lines are 

 seen. These are phenomena seen associated with sodium, but if we 

 use the hydrogen produced from a piece of magnesium wire or from 

 a crystal of olivine, under the same circumstances we find that so far 

 as the lines of hydrogen go the phenomenon remains the same, but 

 that there is then visible in the spectrum a line at 500, which has 

 been recorded in the spectrum of magnesium under other conditions, 

 not only by myself but by Dr. Copeland.* 



* " To this table must be added 500*6 mmm. as the wave-length of the first line in 

 the great band of magnesium as determined by M. Lecoq de Boisbaudran from the 

 spark spectrum of the chloride of that metal, which evidently agrees with the flame 

 spectrum, in this region at least. It is worthy of note tbat this line almost abso- 

 lutely coincides with the brightest line in the spectra of planetary nebula?." 

 (Dr. Copeland, * Copernicus,' vol. 2, p. 109.) 



