THE RECENT PROGRESS OF SOLAR PHYSICS. 3 



observed the periodicity of the spots, and Carrington was already at 

 work, their results were not wholly public, and the facts of the variable 

 velocity of the sun's rotation were rather the surmises of a few than 

 part of the body of acquired knowledge. Since then this branch of 

 astronomy has grown almost to the position of an independent science, 

 and, though it has not yet been distinctly divided into specialties in 

 its turn like its elder sisters, yet we already see a tendency to their 

 formations. Thus, with the study of the motions of the solar surface 

 we associate with the names just mentioned those of Sporer, De la 

 Rue, and Wolf ; with eye-studies of the photosphere or solar meteor- 

 ology, those of Dawes, Secchi, and others ; with the telescopic use of 

 the spectroscope those of Huggins, Janssen, Lockyer, Secchi, Young, 

 and Tacchini. The work of mapping the spectrum, begun by Kirch- 

 hoff, has been continued by Angstrom, Mascart, and Cornu, while pho- 

 tography, in the hands of Rutherfurd, Janssen, and Draper, has largely 

 superseded telescopic studies of the photosphere, and the list might be 

 enlarged indefinitely. Let us glance at part of the work done by these 

 during the past twenty years, for their labors make the history of our 

 study. 



The work of Carrington, completed in 1861, taught us what had 

 before been suspected — both the periodicity of the spots and that this 

 great globe, so far as we can see it, has diflferent periods of rotation, 

 its equatorial zones completing a revolution in less time than its polar 

 ones. We know very little more on this point now, the cause of both 

 phenomena remaining wholly mysterious to-day. 



In the next year (1862) an impulse was given to the study of the 

 solar surface by the announcement of a supposed discovery of gigantic 

 individual bodies in it, of from 500 to 1,000 miles in length, distinct 

 from each other, and existing in countless numbers. This extraordi- 

 nary statement was not easily disproved, as it is with great difficulty 

 that the real structure is discernible by the best telescopes. Forms, 

 we can scarcely call them " bodies," are undoubtedly there, of a size 

 and in numbers which could only exist on so vast a surface, and which 

 are no doubt the chief immediate cause of the sun's light and heat 

 — but what are their causes in turn, and what is their real nature ? 

 The suggestion was made at the time by the then, perhaps, most emi- 

 nent living astronomer, that they might be, in a sort, living things — 

 beings, in fact, whose vital force gave us the solar heat ; a suggestion 

 which we may smile at now, but which was received at the time with 

 a kind of awe, as adumbrating some possible truth. Of its author I 

 would speak with all possible respect in citing it, which I do here, as 

 nothing can better indicate the obscurity of our knowledge, even at so 

 recent a period. We may look back on such a possible suggestion 

 and its connection with that " vital force,'^ now itself banished by 

 physiology, as a kind of landmark on the road we have traveled. Our 

 science, young as it is, is old enough to have had its age of fable. 



