TOTAL ECLIPSES OF THE SUN. 



249 



way on the summit of El Misti, Peru, at an elevation of 19,300 

 feet. At this altitude one-half the earth's atmosphere is below 

 the observer and that which remains is of extraordinary clearness. 

 Photographs were made of the region immediately about the sun, using 

 an opaque disc to protect the plate from the sun's direct image. The 

 true corona did not appear upon the plates. Other methods promised 

 better results, such as the use of monochromatic light, presumably 

 that of the line 'K 1474.' Experiments in this line have been carried 

 on by Professor Hale with skill and enthusiasm on the summit of 

 Pike's Peak, on Mount Etna and elsewhere, but without success. He 

 has also attempted to solve the difficulty by a study pi the heat, using 

 the bolometer. Recent investigations given below explain the failure 



FiG.S. Soi.AK Corona. Eclipse of 1893. Near Scnspot Maximum. Made by Peofessoe 



J. M. SCHAEBERLE, LiCK OBSERVATORY. 



of this method. The polarization of the coronal light also suggests a 

 method which has not vet vielded successful results. Although the 

 future may furnish the solution, none of the attempts yet made has 

 ])een successful, aiid for the present our only knowledge of the corona 

 must be obtained from what can be learned during the brief moments 

 of total eclipses. Good photographs of the corona can be easily and 

 rapidly made and if an abundance of these were alone necessary our 

 knowledge would be well advanced. The general features of the 

 corona have a certain permanence. Comparatively slight changes are 

 known to take place during the three or four hours while an eclipse is 

 passing over the surface of the earth. There may be, however, finer 

 details than are shown on the best photographs jQt obtained, which 



