Mr. J. N. Lockyer on Recent Discoveries in Solar Physics. 155 



to such positions that only the light proceeding from either side of 

 the cyclone can enter it. Then we shall have changes of wave- 

 length in one direction only ; in each case precisely as you see was 

 observed. 



Now let us suppose that instead of a cyclone we have a motion of 

 some portions of the prominence towards the eye, and that, more- 

 over, the rate of motion varies excessively in some portions. What 

 we shall see will be this. The portion of the prominence at rest will 

 give us no alteration of wave-length ; its bright line will be in a line 

 with the corresponding black one in the spectrum. The portion 

 moving towards the eye, however, will give us an alteration of wave- 

 length towards the violet. You are now in a position to grasp the 

 phenomena revealed to me by my spectroscope on the 12th instant, 

 when at times the F line was triple ! the extreme alteration of wave- 

 length being such that the motion of that part of the prominence 

 giving the most extreme alteration of wave-length must have ex- 

 ceeded 120 miles per second, if we are to explain these phenomena 

 by the only known possible cause which is open to us. 



By moving the slit it was possible to see in which part of the pro- 

 minence these great motions arose, and to follow the change of 

 wave-length to its extremest limit. 



By the kindness of Dr. Balfour Stewart I am able to exhibit to 

 you some of the Kew sun-pictures, which show you how these spec- 

 troscopic changes are sometimes connected with telescopic ones. 



On the 2 1 st of April there was a spot very near the limb which I 

 was enabled to observe continuously for some time. At 7.30 a.m. 

 there was a prominence visible in the field of view, in which tremen- 

 dous action was evidently going on, for the C, D, and F lines were 

 magnificently bright in the ordinary spectrum itself ; and as the spot- 

 spectrum was also visible, it was seen that the prominence was in 

 advance of the spot. The injection into the chromosphere surpassed 

 anything I had seen before, for there was a magnesium cloud quite 

 separated from the limb, and high up in the prominence itself. 



By 8.30 the action had quieted down ; but at 9.30 another throb 

 was observed, and the new prominence was moving away with tre- 

 mendous velocity. While this was going on, the hydrogen-lines 

 suddenly became bright on the other side (the earth's side) of the 

 spot, and widened out considerably — indeed to such an extent that 

 I attributed their action to a cyclone, although, as you know, this 

 was a doubtful case. 



Now, what said the photographic record ? The sun was photo- 

 graphed at 10 h 55 m a.m., and I hope you will be able to see on the 

 screen how the sun's surface was disturbed near the spot. A sub- 

 sequent photograph, at 4 h l m p.m. on the same day, shows the limb 

 to be actually broken in that particular place ; the photosphere seems 

 to have been absolutely torn away behind the spot, exactly when the 

 spectroscope had afforded me possible evidence of a cyclone ! 



In connexion with the last branches of the research I have brought 

 to your notice, I may remark that we have two very carefully pre- 



