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. This, surely, is not the just 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 me 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

Soon after, Secchi successfully applied the same method, as did Dr. Huggins, whose spectroscope was, however, not altogether well adapted to the work, having been specially designed for stellar researches.

It was a peculiarity of the new mode of observing the prominence-spectrum that it enabled the observer to determine at his leisure, and in a much more satisfactory manner than had been possible during the eclipse of 1868, the true position of the prominencelines, their characteristics as respects shape (the significance of which feature has been already referred to, p. 146), and also the existence of lines which had escaped observation while the eclipse was in progress. It is obvious that the spectrum of the Sun's limb seen at the same time (or that of the illuminated terrestrial atmosphere) affords the most satisfactory means of determining the position of the bright prominence-lines; for there in the solar spectrum are those very lines—

to the observer. If this were so, the wisest (though most selfish) course which the students of science could follow would be to conceal all original ideas as to modes of observation or processes of research until they could apply those ideas on their own account. The true lover of science cannot do this. He feels bound to publish any such ideas at once, let who will adopt and utilise them (and let who will obtain credit for the result). There may be cleverness in a more diplomatic course, but there is no true love of science.

I may add that as regards the question of priority in this matter more importance might be attached to it were it not well known that after Dr. Huggins's observations of T Coronæ, the principle on which the new mode of observation rests was recognised by all who understand spectroscopic analysis. Like the discovery of Sun-spots, therefore, this recognition of the prominence-lines in full daylight was an inevitable sequel of the construction of an adequately dispersive spectroscopic battery.

the dark lines C and D and F, and so on-with which the eclipse observers had associated the bright lines. It is only necessary to see whether those dark lines coincide in position with the bright ones (see figs. 36, 37, and 38, in which, however, but a few dark lines are shown) in order to tell whether the bright prominence-lines are or are not due to the presence of those particular elements to which the solar dark lines belong.

Janssen found in this way that the orange line of the prominences does not correspond, as had been thought, with the D or sodium (double) line of the solar spectrum. He found, however, that the red and blue prominence

lines do actually coincide with the C and F lines of hydrogen. So that these enormous objects, extending in some instances to a height of more than 80,000 miles above the Sun's surface, consist in part, at least, of the glowing vapour of hydrogen.

But it was possible to recognise other lines besides these three by the new method, when an instrument of adequate dispersive power was employed. The accompanying picture (fig. 72), for example, exhibits the spectrum of a prominence, and of the adjacent portion of the Sun's limb, as shown by Mr. Lockyer's

spectroscope. It will be seen that the double line of sodium as well as three lines of the magnesium spectrum are shown. It is only necessary to suppose that M. Rayet saw the two close double lines as single ones in order to account exactly for the nine lines seen by him.*

* The following is Fr. Secchi's description of the principal lines seen in the prominence-spectrum under ordinary conditions:

'The line c of hydrogen,' he says, 'is the most easily seen of all. It sometimes reaches the enormous height of three minutes, indicating the presence of such colossal prominences as are seen during eclipses. On the limb of the Sun generally the height of this line is very irregular, and on the average attains to from ten to fifteen seconds. This line also extends in a well-marked manner within the limb, overlapping the disc by ten seconds and more. Yet further on the disc there is a region where the line cannot be seen, being neither bright nor dark, but of the same tint exactly as the neighbouring part of the spectrum, which is thus in this part of its length continuous and uniformly bright. With a slit placed parallel to the limb the space throughout which the line disappears is often considerably extended. Outside the disc the line is much brighter near its base than at the summit, and the line is dilated at the base, and seems to terminate in a point where its light fades off, until, as I have already said, it becomes of the same brightness as the neighbouring part of the spectrum before becoming a dark line. Outside the Sun the line is bounded by two dark lines, which appear at first sight to be the effect of contrast, but may probably have another and a real cause. The bright line is often formed of knots and separate pieces, which are evidently so many fragments of different prominences, placed one beyond the other and unequally bright. If the aperture of the slit be enlarged as much as is possible without rendering the light unbearable, the bright line of the rose-coloured fringe is seen to be marked by irregularities which are due to the roughness of texture (scabrosità) of the prominences themselves.'

After mentioning that he has been able to apply Janssen's method of determining the shape of the prominences by taking line-sections Secchi remarks that he has often tried to determine whether there is any fixed law as regards the direction in which the prominences are bent, but has hitherto not succeeded in tracing any.

'The line in the yellow, near the sodium lines, is about twice and a half as far from the nearest of these as these are from each other. This

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