ADDRESS. XCVll 



racter, wliicli, noAV that the necessity of tlie interposition of the moon -was 

 dispensed with, coiild be traced complctclj^ round the sun. Notices of this 

 discovery were received from the author by the lioyal Societ}'- on October 21 

 and November 3, and the former was ahnost immediately published in No. 105 

 of the Proceedings. These were shortly afterwards followed by a fuller paper 

 on the same subject. 



Meanwhile the same thing had been independently observed in another 

 part of the world. After having observed the remarkable spectrum of the 

 prominences during the total eclipse, it occurred to IT. Jaussen that the same 

 method might allow the prominences to be detected at any time ; and on trial 

 he succeeded in detecting them the very day after the ecHpse. The results of 

 liis observations were sent by post, and were received shortly after the 

 account of ilr. Lockyer's discovery had been communicated by Mr. De La Hue 

 to the French Academy. 



In the way hitherto described a prominence is not seen as a whole, but 

 the observer knows when its image is intercepted by the slit ; and by vary- 

 ing a little the position of the slit a series of sections of the prominence are 

 obtained, by putting which together the form of the prominence is deduced. 

 Shortly after Mr. Lockyer's communication of his discovery, Mr. Huggins, 

 who had been independently engaged in the attempt to render the promi- 

 nences visible by the aid of the spectroscope, siicceeded in seeing a pro- 

 minence as a whole by somewhat •svidening the slit, and using a red glass to 

 diminish the glare of the light admitted by the slit, the prominence being 

 seen by means of the C line in the red. Mr. Lockyer had a design for see- 

 ing the prominences as a whole by giving the slit a rapid motion of small 

 extent, but this proved to be superfluous, and they are now habitually seen 

 with their actual forms. Nor is our power of observing them restricted to 

 those which are so situated that they are seen by projection outside the sun's 

 limb ; such is the j^ower of the spectroscopic method of observation that it has 

 enabled Mr. Lockj-er and others to observe them right on the disk of the sun, 

 an important step for connecting them with other solar phenomena. 



One of the most striking results of the habitual study of these prominences 

 is the evidence they afford of the stupendous changes which are going on in 

 the centi'al body of our system. Prominences the heights of which are to be 

 measiired by thousands and tens of thousands of mUes, ajipear and disappear 

 in the course of some minutes. And a study of certain minute changes of 

 position in the bright line F, which receive a simple and natural explanation 

 by referring them to proper motion in the glowing gas by which that line is 

 produced, and which we see no other way of accounting for, have led Mr, 

 Lockyer to conclude that the gas in question is sometimes travelling with 

 velocities comparable with that of the earth in its orbit. Moreover these ex- 

 hibitions of intense action are frequently found to be intimately connected 

 with the spots, and can hardly fail to throw light on the disputed question 

 of their formation. Nor are chemical composition and proper motion the only 

 physical conditions of the gas which are accessible to spectral analysis. Ey 

 comparing the breadth of the bright bands (for though narrow they are not 

 mere lines) seen in the prominences with those observed in the spectrum of 

 hydrogen rendered incandescent under different phj'sical conchtions. Dr. 

 Fraukland and Mr. Lockyer have deduced conchisions respecting the pressure 

 to which tlie gas is subject in the neighbourhood of the sun. I am happy to 

 say that Mr. Lockyer has consented to deliver a discourse during our Meeting, 

 in which the whole subject will doubtless be fully explained. 



I have dwelt perhaps too long on this topic, and I cannot help fearing that 

 18:J9. g 



