io8 



Progress in Physics* 



[January, 



Fig. 12. 



path passed over by this cloud was more than 90,000 miles, and the velocity 

 above 120 miles per second. Fig. 12 represents a prominence observed 



September 20th, at 4 p.m., on the S.E. limb. 

 (Pos. S., 6o° E.) It was a nearly vertical 

 stream, made up of spindle-formed filaments, 

 and had attained the enormous height of 

 3' 20", or 90,000 miles (determined, as in the 

 case above mentioned, by a time observation, 

 corrected for inclination). It was very 

 brilliant near the base, and at two or three 

 other points along its length. At 4.30 it was 

 nearly gone, only a few faint wisps of cloud 

 remaining. Another observed on September 

 27th, at 4.10 p.m., and situated on the W. 

 limb of the sun, is represented in Fig. 13. It 

 was formed of separate, well-defined narrow 

 streamers, which appeared to consist of 

 matter, first violently ejected, and then as 

 violently deflected, by some force acting nearly 

 at right angles. The altitude of the highest 

 point was i' 25", the length of the whole about 

 3' 30". 



Bright Lines. — In the spectra of different 

 protuberances, the following bright lines have 

 been observed, the numbers referring to 

 Kirchhoff's scale: C; Y) 1 ; D 2 ; D 3 ; 1474; 1515 ; b z ; b 2 ; b 3 ; b A ; 1990; 

 2001; 2031; F; 2581-5; 2796; h — 17 in all. On one occasion, September 

 27th, the base of a prominence on the N.W. limb,, close to a spot just leaving 

 the limb, exhibited as many as twelve or fifteen short bright lines between E 

 and F, which are not included in the above enumeration. The line, 2581*5, 

 which was conspicuous at the eclipse of 1869, seems to he always present in the 

 spectrum of the chromosphere, and shows the form of its upper surface or of a 

 protuberance nearly as well, though not so brightly, as the 2796 line. It has 

 no corresponding dark line in the ordinary solar spectrum, and, not improbably, 

 may be due to the same substance that produces D 3 . The reversal of the 

 sodium and magnesium lines is not at all uncommon. In some instances 

 these lines were so bright that, on opening the slit, the form of the prominence 

 could be made out through them. This was the case with a small hand-shaped 

 prominence observed on September 27th. Comparing the form thus seen 

 through Dj and D 2 , with that given by D 3 , it appeared that the sodium line 

 was sufficiently developed for observation only along the edge and at one or 

 two bright points in the prominence, most brilliantly neither at its summit nor 



Fig. 13. 



Fig. 14. 



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mmut < '» «AM 



its base. Fig. 14 represents the appearance (the slit was perpendicular to the 

 sun's limb). The case was similar with the magnesium lines. 



Spectrum of Solar Spots. — The most interesting phenomena were exhibited 

 by a large group, which was first observed near the E. limb on September 19th. 

 Changes of wave length were frequent in its neighbourhood. Figs. 7 and 8 



