4 THE POPULAR SCIENCE MONTHLY. 



Since that time, in France, in Italy, in England, and here, thou- 

 sands of telescopic studies have been made with the purpose of defin- 

 ing these forms, and of learning more about the growth of those 

 mysterious objects with which they are associated — the sun's spots, 

 which drew the attention of Fabricius and Galileo, and which still 

 attract our own more than ever to-day, with problems which seem 

 nearly insoluble. Everything we see convinces us that the solar sur- 

 face in which they are formed is neither a solid nor a liquid, but com- 

 posed of volumes of whirling vapors ; yet through this vapor, which 

 seems to offer no resistance, come eruptions of explosive violence such 

 as one would suppose must arise from the sudden bursting of some 

 rigid shell. The turmoil within the areas of disturbance is so great, 

 the area itself so vast and inclosing such diversities of action, that we 

 are still doubtful how far this action is downward, how far upward. 



Under the. circumstances, we can hardly say that twenty years of 

 observation in this department have brought us results commensurate 

 with the labor expended, nor have we derived great aid from photo- 

 graphy until some recent advances of which I have presently to speak. 



A review of our past studies of the corona is a review of the solar 

 eclipses during the past twenty years ; for it is a fact, unparalleled in 

 the sciences of observation, that the opportunities for this knowledge 

 last only minutes, and are separated by intervals of years. Till 1860 

 it was uncertain whether the protuberances belonged to the sun or 

 moon, but in that year the then newly applied photographic method 

 made it nearly certain that they were parts of the former, and previous 

 surmises that they were extensions of an envelope everywhere sur- 

 rounding the sun were confirmed. In 1868 some traces of the corona 

 were first photographed. The spectroscope was used upon the promi- 

 nences, their gaseous nature was proved, and nine of the chromospheric 

 lines were determined ; and nearly together Messrs. Janssen and Lock- 

 yer made the discovery that these lines could be seen without an 

 eclipse ; 1869 brought that eclipse which traversed our own territory, 

 and in this the distinctive coronal line was first observed by Young 

 and by Harkness ; while in this, and yet more in the eclipse of 1870 

 and 1871, we obtained better photographs of the corona, and greatly 

 increased our knowledge of its apparent structure. 



It is hardly possible to present even in the briefest way any review 

 here of the separate history of spectroscopic reseai'ch since 1860, 

 during which time it has been connected with most of the important 

 steps in every field of our study. It has, in the hands of Messrs. Hug- 

 gins, Zollner, and Young, made visible to us the forms of the chromo- 

 sphere, and enabled us to measure the velocity of motions upon the 

 sun otherwise beyond estimate, while at the same time it has given us 

 independent data for the absolute velocity of other suns in space, and 

 for that of the rotation of our own solar photosphere. It has, in the 

 hands of Secchi and others, connected our knowledge of our sun's 



