latter portion of Chapter III. Briefly re-stated it is this: The light of the prominences when dispersed by the spectroscope forms a few lines; that of the illuminated terrestrial atmosphere is spread out into the rainbow-tinted solar spectrum. Therefore, if we only use adequate dispersive power, we can cause the prominence-lines to show conspicuously on the background of dispersed atmospheric light.

Clouds which gathered over the face of the Sun soon after totality prevented M. Janssen that day from pursuing this idea. But on the morrow he applied it with complete success. 'I have experienced,' he said, 'to-day a continuous eclipse.'

We have seen how it becomes possible by this method not only to recognise the spectrum of a prominence during full daylight, but by a series of sectional views, so to speak, to determine the figure of a prominence. To this work Janssen applied himself, and he was presently able to forward to Europe news of his complete success in this new branch of research.

The news of this important discovery was nearly two months in reaching Europe, and a few days before it arrived Mr. Lockyer had independently obtained a similar result. The history of his work and of the way in which it was suggested is not without interest. In May 1866, Dr. Huggins had examined the spectrum of the star which blazed out suddenly in that year in the constellation Corona. He found that this starnow known as T Coronæ *-gave a spectrum which

* In Mr. Roscoe's valuable work on spectroscopic analysis, this star

differed altogether from any he had previously examined. There was the rainbow-tinted streak crossed by dark lines which ordinarily forms the spectrum of a star; but over this, and obviously corresponding to a large proportion of the star's light, there were bright lines. These bright lines corresponded in position with the lines belonging to hydrogen; so that Dr. Huggins was able to pronounce that the great increase in the star's light was due to an outburst of glowing hydrogen. Afterwards he found that other stars, and notably the middle star in the conspicuous W group of Cassiopeia, show bright lines, superposed on the rainbow-tinted background, though relatively far less bright than those seen in the spectrum of T Coronæ. In these cases, also, the lines were those of glowing hydrogen.

Here, then, was a perfectly apt illustration of the principle dwelt on in the concluding part of Chapter III. Here were the lines of a certain element rendered separately visible as bright lines, though the total amount of light received from the glowing hydrogen was not necessarily (in the case at least of the star in Cassiopeia) equivalent, or nearly so, to the remaining portion of the star's light. The concentration of the light into three definite lines enabled it to

is always referred to as 7 Coronæ. This is a mistake. The star 7 Coronæ is a well-known fifth-magnitude star towards the north of the constellation. The real variable (ordinarily a tenth-magnitude star) lies to the south of all the conspicuous stars of Corona. It is called T in accordance with the rule by which the variables successively discovered in a constellation are named from the last letters of the alphabet, beginning with R.

prevail, as far as intrinsic brightness was concerned, over the diffused light, absolutely greater in amount, which formed the rainbow-tinted streak.

We cannot wonder, therefore, that the idea should at once have been suggested that if any portions of the Sun-as, for example, the coloured prominences-consist of glowing gas, the spectrum of such portions might be recognisable even amidst the spectrum of the far more intense light (so far as absolute brightness is concerned) of the solar photosphere.

Mr. Lockyer was preparing about this time to undertake a careful scrutiny of the photosphere with more powerful spectroscopic appliances than had yet been employed. Amongst the expectations which he formed at that time, there is a reference to the problem presented by the prominences. It may be interesting to give at full length the concluding words of the paper he addressed to the Royal Society :

'Seeing that spectrum analysis has already been applied to the stars with such success, it is not too much to think that an attentive and detailed spectroscopic examination of the Sun's surface may bring us much knowledge bearing on the physical constitution of that luminary. For instance, if the theory of absorption be true (!) we may suppose that in a deep spot rays might be absorbed which would escape absorption in the higher strata of the atmosphere; hence, also, the darkness of a line may depend somewhat on the depth of the absorbing atmosphere. May not also some of the variable lines visible in the solar spectrum be due

to absorption in the region of the spots? and may not the spectroscope afford us evidence of the existence of the red-flames' which total eclipses have revealed to us in the Sun's atmosphere, although they escape all other methods of observation at other times? and if so may we not learn something from this of the recent outburst of the star in Corona?'

It does not appear quite clearly from this passage whether Mr. Lockyer expected (as De La Rue had before) to find traces of the prominences, when examining the Sun's surface, or whether it fell in with his plans to examine outside the Sun's disc. But the latter is the more probable explanation. The grant he asked for from the Royal Society was allowed him, and the construction of a suitable spectroscope was entrusted to Mr. Browning (after a delay consequent on the death of Mr. Cooke). In the meantime Dr. Huggins applied his spectroscope unsuccessfully to the search, and Fr. Secchi, who had thought of examining the Sun's edge, gave up the attempt on hearing of Mr. Lockyer's failure to detect anything remarkable there.*

Whether, supposing no further discoveries had been made, Mr. Lockyer would have succeeded in recognising the bright lines of the prominences, is one of those questions which never can be answered. For

Era già gran tempo che avevamo intenzione di esplorare l'orlo del sole con lo spettroscopio, ma l'assicurazione data da molti abili osservatori e dal Sig. Lockyer stesso, che nulla vedevasi di più all' orlo del disco che al centro, ce ne avea distolto.'-Memoria III. sugli spettri prismatici de' corpi celesti.

my own part, I cannot but think that he would assuredly have succeeded in the long run, even if the Indian expedition had been a failure. My reason for believing this is that Mr. Browning had so successfully mastered the optical conditions of the problem as to ensure complete success on the observer's part, whenever the examination of the Sun's limb should be thoroughly undertaken. However, owing to one cause and another, there ensued considerable delay before Mr. Lockyer attempted to make the required observations; and in the meantime news came to England that the spectrum of the prominences included three conspicuous bright lines. This placed it out of Mr. Lockyer's power to discover the lines; but it was still left for him to show that they can be seen when the Sun is not eclipsed. Two months after the eclipse he announced that he had so seen them; and the story runs that some five minutes or so before, the announcement of Janssen's prior success had been received by the President of the Imperial Academy at Paris, a communication from Mr. Lockyer to a similar effect had been read to that learned body.*

* M. Faye, while admitting Mr. Lockyer's claim to the independent recognition of the visibility of the lines without eclipse, expresses a feeling of regret that the mere distance between India and Europe should have prevented France-as represented by M. Janssen-from enjoying the full credit of the discovery. There is something almost childish in this mode of viewing the matter. How M. Janssen's credit can be diminished because Mr. Lockyer independently effected the same observation it would be hard indeed to say. But this is not all. It seems to us that nothing can be more mischievous to science than the promulgation of the idea that mere priority in making and announcing an observation is to afford the chief measure of the credit to be assigned