SOLAR ECLIPSE EXPEDITIONS— MITCHELL ]^53 



the south point of the sun. Intertwining the coronal streamers was 

 a beautiful series of coronal domes connected with an extended promi- 

 nence group. Greater heights were attained by another group of 

 prominences, at position angle 115°, the location of a conspicuous 

 feature called the "strawberry dome," with its magnificent arches and 

 delicate structure of filamentous details. On plate 4, drawings near 

 this particular dome are given for comparison; at A from the K and 

 Ha lines of the spectra of the chromosphere, at B three drawings of 

 the same region from the direct photographs and from the lines 5303 

 and 6374 of coronium, respectively. At C on the western edge of the 

 sun, the details in the green coronal line at 5303 result in forms 

 similar to the coconut palms that grow so profusely on "Tin-Can" 

 Island. 



For many years eclipse observers have called attention to the con- 

 nection between coronal streamers and prominences. This depend- 

 ence was abundantly verified in 1930, but this eclipse demonstrates the 

 fact that the longest coronal streamers, on which the shape of the 

 corona more or less depends, are always located near prominences but 

 are not necessarily exactly connected with the prominences which at 

 the time of the eclipse are of the greatest height. 



PHOTOGRAPHING THE CORONA OUTSIDE OF AN ECLIPSE 



In 1882, when a bright comet was seen close to the eclipsed sun, 

 attempts were started to photograph the corona without waiting for 

 an eclipse. A decade later, the spectroheliograph was developed, and 

 prominences were readily photographed in full sunshine with the 

 result that attempts were renewed on the corona. In order that the 

 glare of the earth's atmosphere be reduced as much as possible, 

 mountain tops like Pike's Peak or Mount Etna were occupied. No 

 success whatever being obtained, a series of attempts were made by 

 heat-measuring instruments lilte bolometers or photoelectric cells. 

 Each and every one of the plans, at times carried out with great skill 

 and ingenuity, resulted over and over again always in the same man- 

 ner — failure to photograph the corona. The measures made by 

 Abbot in 1908 and by many others since then have shown the cause 

 of the failures, namely, the intrinsic feebleness of the coronal light. 

 Even in its brightest parts, the inner corona is no brighter than the 

 surface of the full moon. The corona is about equal to the intensity 

 of the illuminated sky at 8° or 10° away from the sun's edge. 



In 1930 and in later years Lyot of the Meudon Observatory has 

 had brilliant successes where others had repeated failures. His great 

 triumph resulted from the ingenious arrangement of his telescope to 

 reduce to a minimum the amount of scattered light inside the instru- 

 ment. A mountain observatory on the Pic du Midi (9,100 feet) and 

 at times very transparent skies permitted photographs when the 



