Prismatic Spectra of the August Meteors. 163 



in the field of view of the meteor spectroscope as that which 

 they occupy in the sky to the unassisted eye. In this manner 

 the instrument is well adapted for analysing the light of any 

 bright object presenting itself for a moment in the part of the 

 sky under examination, as, for example, the light of a shooting- 

 star, or of its bright, fast-fading luminous train. 



A flame of mono-chromatic light, or of light possessing 

 only one degree of refrangibility presents, when viewed in the 

 meteor spectroscope, a striking aspect. The flame of a common 

 spirit-lamp, for example, possesses a faint and hardly distin- 

 guishable spectrum. Its light, when viewed through the 

 instrument, is so dispersed, in a horizontal direction, as to be 

 almost washed out, or obliterated ; but if salt be introduced 

 into the wick, the flame at once becomes conspicuous, and the 

 homogenous character of its light is perceived by the sharp- 

 ness of the definition, every flicker of its outline being visible, 

 as perfectly and as brightly as it appears to the naked eye* 

 The example of the spirit-lamp with a salted wick illustrates 

 the streaks of some of the August meteors, which, when 

 examined optically by the meteor spectroscope, reveal their 

 chemical character from the composition of their light. 

 Seventeen spectra were observed, in eight of which the sodium 

 line, for the most part brilliant, and in some cases forming 

 the entire spectrum of the streak, was plainly visible. Its 

 position relatively to the rest of the spectrum, " on the side 

 towards the red" (Nos. 9, 12, and 14), its golden yellow 

 colour (Nos. 7, 8, 12, 14), its extreme brightness (Nos. 7, 14), 

 and its single or isolated appearance (Nos. 8, 14) perfectly 

 agree with the well-known appearance in the spectroscope of 

 the yellow sodium flame ; and at the same time with the 

 spectrum of no other elementary substance, sodium only ex- 

 cepted, with which the spectroscope has made us acquainted. 

 That the element sodium should be the first detected in the 

 meteor spectra is by no means surprising, when the well- 

 known brightness of this line of the spectrum is considered, 

 wherever a trace of sodium exists in the outer luminous 

 envelope of a flame. Nevertheless the fact, that the sodium 

 line has been observed in the spectrum of lightning, is no 

 proof that the meteor-streaks owe its presence in their light to 

 the existence of the vapour of sodium in the atmosphere. No 

 lines of nitrogen, or of any other known gas, accompany the 

 sodium flame in the train spectra of the August meteors ; but 

 on the other hand the great intensity of the sodium streaks 

 makes it almost certain that the meteors contain this element 

 as a part and parcel of their chemical composition. 



To obtain the spectra of meteors, a night must be chosen 

 when they are more than ordinarily plentiful (such as, for 



