60 THE INDIAN ECLIPSE, 1898. 



nothing of the gas indicated by this line, for it has not been 

 discovered in any terrestrial substance; it has, however, been 

 named provisionally, for the sake of convenience of reference, as 

 " coronium." Eclipse work, therefore, at the present day usually 

 includes in its programme the determination of the variation in 

 relative intensity of these three sources of coronal light from 

 one eclipse to another ; the record and measurement of the 

 positions of the bright coronal lines, and their identification, 

 if possible, with terrestrial elements ; and the distribution in the 

 corona and round the sun, of the various bright lines of the 

 coronal spectrum, and especially of the line " 1474 K," the line 

 of " coronium." 



From the first beginning of spectroscopic astronomy it was 

 seen that the actual " photosphere," or bright surface of the 

 sun, sent us light of every conceivable colour in other words, 

 would give us, if we could see it alone, a spectrum perfectly 

 continuous, without dark line or break, from red to violet. 

 The dark Fraiinhofer lines were due to the absorptive action of 

 gases closely surrounding the sun, and stopping out certain rays 

 of definite colour or refrangibility. These gases being intensely 

 heated, would, could we see them apart from the sun, give 

 us discontinuous spectra of separate bright lines. Since, then, 

 these gases, when the sun is viewed through them, cause the 

 appearance of dark lines in its spectrum, they have been spoken 

 of as " the reversing layer." 



Up to the eclipse of 1870, December 22, the spectrum of 

 these gases had not been separately seen. But on that occasion 

 Professor C. A. Young, watching the spectrum of the dwindling 

 arc of sunlight with a slit spectroscope, as the moon had all 

 but hidden the sun, saw at the moment of second contact the 

 ordinary solar spectrum with its dark lines on the continuous 

 background disappear, and then " all at once, as suddenly as a 

 bursting rocket shoots out its stars, the whole field of view was 

 filled with bright lines, more numerous than one could count." 

 This beautiful appearance has since become known as the 

 " Flash." 



The interpretation w T hich Professor Young put upon this 

 observation was that he had seen the spectrum of the " reversing 

 layer." " Of course it would be very rash," he says, " on the 

 strength of such a glimpse to assert with positiveness that these 

 innumerable lines corresponded exactly with the dark lines of the 

 spectrum which they replaced, but I feel pretty fairly confident 

 that such was the case." This would mean that the dark lines 

 which we see in the ordinary spectrum of the sun were due to 

 the absorption of a comparatively thin shell of gases surrounding 

 it, the spectrum of which we can only secure on such occasions 

 as these. 



It has therefore been a point much desired to secure a 



