THE 



POPULAR SCIEKCE 

 MONTHLY. 



NOVEMBER, 1879. 



THE EECENT PEOGKESS OF SOLAE PHYSICS.* 



By Professor' S. P. LANGLEY, 



OF THE ALLEGHENY OBSEEVATOEY. 



LEAVING to those of wider knowledge the survey of the whole 

 field of scientific labor, it has seemed to me that I could best 

 present to you some account of that branch of it with which I am 

 most familiar, which is that of "Solar Physics." 



This study is essentially a modern one. Astronomy, which in the 

 earliest times could only mark the annual path of the sun, or count 

 the stars, with the invention of the telescope still concerned itself 

 more with the motions of the heavenly bodies than with their physi- 

 cal nature. It sought out new methods of precision to fix the places of 

 these stars and to mark out for the navigator the path of the moon on 

 the celestial dial ; it united itself intimately with the sister science of 

 mathematics in predicting the places of the heavenly bodies from the 

 law of gravitation, but it was still as a surveyor and marker of boun- 

 daries in the field of space that the observer chiefly labored, and we 

 associate the most striking triumphs of the classic astronomy with this 

 work of precision. It is this aspect that appeals even to the imagi- 

 nation, and which is seized as distinctive by the poet of Urania : 



" That little Vernier on whose slender lines 

 The midnight taper trembles as it shines, 

 Tells through the mist where dazzled Mercury burns, 

 And marks the spot where Uranus returns." 



These are noble aims, and noble results ; but it is curious to see 

 how observers of the last century, who had learned this excellent lesson 



* Address before the Phj-sical Section of the American Scientific Association at Sara- 

 toga 



TOL. XTI. — 1 , 



