ON THE SOLAR ECLIPSE OF DEC. 12, 1871. 331 



train of prisms, pure and simple, using the corona as tlie sKt, a large number 

 of prisms being necessary to separate the various rings we hoped to see, by 

 reason of their strong dispersion. 



This principle, good for a train of prisms such as I have referred to, is 

 good also for a single prism in front of the object-glass of a telescope. Such 

 -was the method adopted by Prof. Eespighi, the distinguished Director of the 

 Observatory of the Capitol of Rome, who accompanied the expedition. 



This method, if it succeeded, would be superior to the ordinary one in this 

 way. If we were dealing merely with scattered light, then aU the rings 

 formed by vapours of equal brilliancy at the base of the chromosphere would 

 be of the same height ; while if such scattering were not at work, the rings 

 would vary according to the actual height of the vapours in the sun's 

 atmosphere. 



3. Integrating spectroscopes driven hi/ clockwork. 



4. A self-registering integrating spectroscope, furnished with telescopes 

 and collimators of large aperture and large prisms. (This instrument was 

 lent by Lord Lindsay.) 



5. A polariscope-telescope so arranged that the same observer could almost 

 simultaneously observe both with the Savart and the Biquartz. 



6. A polariscope-telescope arranged for rapid sweeping round the corona 

 at a given distance from moon's limb. 



II. The Main Resttlts. 

 Spectroscopic Observations, 



It has been established that the idea that we do not get hydrogen above 

 10" above the sun is erroneous, for we obtained evidence that hydrogen exists 

 to a height of 8' or 10' at least above the sun. 



Just as the sun disappeared Prof. Respighi employed the instrument to 

 which I have already referred to determine the materials of which the pro- 

 minences which were then being eclipsed were composed; and he got the 

 prominences shaped out in red, yellow, and in violet light, a background of 

 impure spectrum filling the field ; and then as the moon swept over those 

 prominences they became invisible. He saw the impure spectrum and the 

 yeUow and violet rings gradually die out, and then three broad rings, painted 

 in red, green, and blue, gradually form in the field of view of his instrument ; 

 and as long as the more brilliant prominences on both sides of the sun were 

 invisible he saw these magnificent rings. 



These rings were formed by C and F, which show us that hydrogen 

 extends at least V high ; for had we been dealing with mere glare, had we 

 not been dealing with hydrogen itself, we shotdd have got a yellow ring as luell. 

 In addition to the red ring and the blue and violet, which indicate the 

 spectrum of hydrogen, he saw a bright green ring, much more brilliant than 

 the others due to 1474. 



While Prof. Respighi was observing these rings by means of a single prism 

 and a telescope of some 4 inches aperture, some 300 miles away from him 

 (he was at Poodocottah and I was at Bekul) I had arranged the train of five 

 prisms. My observation was made intermediately, as it were, between 

 the two observations of Prof. Respighi's. The observations may be thus 

 compared : — 



Respighi ..CD' F G . . . . Prominence at beginning of eclipse. 



Lockyer . . C 1474 F G .... Corona 80" after beginning of totality. 



Respighi . . C 1474 F .... Corona mid eclipse. 



