THE LOWELL OBSERVATORY ECLIPSE OBSERVA- 

 TIONS, JUNE 8, 1918. 



Prominences and Coronal Arches. 



By C. O. LAMPLAND. 

 (Read April 2S, W^Q-) 



The solar prominences or protuberances have considerable his- 

 torical interest in the part they have taken in the advances made in 

 our knowledge of the constitution of the sun. These beautiful 

 formations, varying in color from deep ruby to pale pink, project- 

 ing outside of the dark disk of the moon upon the background 

 of the pearly luster of the corona at times of totality caught the 

 attention of earlier observers and we may have references to 

 them extending back two hundred years. They came to occupy a 

 conspicuous place in the eclipse literature of 1842, and Dr. Lockyer 

 remarks of this eclipse in connection with the prominences, " then 

 the golden age begins." But whether they belonged to the moon 

 or the sun was a question that was not definitely decided until De la 

 Rue's photographic observations of the eclipse of i860. His series 

 of exposures during totality showed beyond doubt that the promi- 

 nences on the opposite edges of the sun were progressively covered 

 and uncovered by the disk of the advancing moon. At the present 

 day it may help us to sympathize with the difficulties of these earlier 

 investigators to recall our own helplessness, and how we are appar- 

 ently marking time, on some of the outstanding problems of the 

 corona. 



Our knowledge of the more complex structure of the inner 

 corona by direct observations has been largely obtained by photog- 

 raphy, and noteworthy progress has been achieved during the last 

 twenty-five years. Large-scale photographs, suitable sensitive 

 plates, and graduated series of exposures may be mentioned among 

 some of the things that have contributed to the advances made. 



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