138 



Anniversary Meeting. 



[Nov. 30, 



been seen from the earliest times ; but what does it import ? Has it its 

 seat in our own atmosphere, or in an atmosphere of the moon, or in some- 

 thing surrounding the sun ? and, in the latter case, is it self-luminous, or 

 does it shine by reflected light? What, again, is the nature of those 

 singular rose-coloured luminous objects seen just outside the dark disk of 

 the moon, which were first brought prominently into notice by the obser- 

 vers who watched the eclipse of July 7, 1842, and have subsequently been 

 seen on the occasion of total solar eclipses ? 



Evidence bearing in an important manner on the true answers to these 

 questions had already been obtained on the occasion of former total eclipses. 

 In that of July 18, 1860, M. Prazmouski ascertained that the light of the 

 corona was strongly polarized iu a plane passing through the centre of the 

 sun, while that of the prominences was unpolarized. The fact of the polari- 

 zation discarded the hypothesis, sufficiently improbable on other grounds, 

 that the corona belongs either to our own atmosphere or to a lunar atmo- 

 sphere (since in that case the light would be reflected or scattered at an 

 almost grazing incidence), and proved it to belong to the sun, and to shine 

 mainly, if not wholly, by reflected light. The absence of polarization in 

 the light of the prominences proved that they are very probably self- 

 luminous. The elaborate photographic observations of Mr. Warren De La 

 Rue on the same eclipse proved, by the motion of the prominences rela- 

 tively to the moon, that they belong to the sun, and showed that their light 

 is remarkable for its actinic power. 



In the interval between this eclipse and that of the present year,^a neV 

 method of research had sprung up, in the application of the spectroscope to 

 the celestial bodies, and already, in the hands of Mr. Huggins, had revealed 

 in many of the nebulae a constitution hitherto unsuspected. It was impor- 

 tant to apply this method of research to the red prominences. Should they 

 give a continuous spectrum, the conclusion would be that the matter of 

 which they consist is probably in a solid or liquid condition, such as 

 clouds formed by precipitation; should the spectrum be one of bright 

 lines, we must conclude that they are glowing gas. 



To solve this important problem, independently of what might be done 

 by other scientific bodies or by individuals, the Royal Society procured an 

 equatorially mounted telescope, furnished with a spectroscope and clock- 

 movement. With the sanction of Colonel Walker, R.E., Director of the 

 Great Trigonometrical Survey of India, this instrument was entrusted to 

 Lieut. John Herschel, R.E., who is attached to the Survey, and who, 

 being at the time in England, had the advantage of instruction from so 

 skilful an observer as Mr. Huggins before his return to India. After his 

 return to India, Lieut. Herschel worked diligently at the spectra of the 

 southern nebulae, thereby at the same time making an important addition 

 to our knowledge, and practising for the approaching eclipse. Four direct- 

 vision hand-spectroscopes, intended for distribution to observers at dif- 

 ferent stations, were also sent out, — partly that the occasion might not be 



