ON THE PROGRESS OP SCIENCE. v 



poraries, and enabled them to ascertain the time of its rotation, and 

 the inclination of its axis. They also correctly inferred, from their 

 appearance, the existence of a luminous envelope, in which funnel- 

 shaped depressions revealed a solid and dark nucleus. Just a century 

 ago, Alexander Wilson indicated the presence of a second and less 

 luminous envelope beneath the outer stratum ; and his discovery was 

 confirmed by Sir William Herschel, who was led to assume the pres- 

 ence of a double stratum of clouds, the upper intensely luminous, the 

 lower gray, and forming the penumbra of the spots. Observations 

 during eclipses have rendered probable the supposition that a third 

 and outermost stratum of imperfect transparency encloses concentri- 

 cally the other envelopes. Still more recently, the remarkable discov- 

 eries of Kirchhoff and Bunsen require us to believe that a solid or liquid 

 photosphere is seen through an atmosphere containing iron, sodium, 

 lithium, and other metals in a vaporous condition. 



"Magnetism. Guided by the same principles which have been so 

 successful in Astronomy, its sister science, Magnetism, emerging from 

 its infancy, has of late advanced rapidly in that stage of development 

 which is marked by assiduous and systematic observation of the phe- 

 nomena, by careful analysis and presentation of the facts which they 

 disclose, and by the grouping of these in generalizations, which, when 

 the basis on which they rest shall be more extended, will prepare the 

 way for the conception of a general physical theory, in which all the 

 phenomena shall be comprehended, whilst each shall receive its sepa- 

 rate and satisfactory explanation. 



" To refer to a single instance of the elucidation of magnetic phe- 

 nomena, we have seen those magnetic disturbances so mysterious in 

 their origin, and so extensive in simultaneous prevalence, and which 

 less than twenty years ago were designated by a term specially denot- 

 ing that their laws were wholly unknown traced to laws of periodi- 

 cal recurrences ; revealing, without a doubt, their origin in the central 

 body of our system, by inequalities which have for their respective 

 periods the solar day, the solar year, and, still more remarkably, an 

 until lately unsuspected solar cycle, of about ten of our terrestrial 

 years, to whose existence they bear testimony, in conjunction with the 

 solar spots, but whose nature and causes are in all other respects still 

 wrapped in entire obscurity. We owe to General Sabine, especially, 

 the recognition and study of these and other solar magnetic influences, 

 and of the magnetic influence of the moon, similarly attested by con- 

 current determinations in many parts of the globe, which are now held 

 to constitute a distinct branch of this science, not inappropriately named 

 celestial,' as distinguished from purely terrestrial magnetism. 

 1* 



