252 CARNEGIE INSTITUTION OF WASHINGTON. 



conclusive. The plates are now being measured with the Koch regis- 

 tering micro-photometer, which should give much more reliable results 

 than visual measures. It is evident that even if no positive effect can 

 be found, it will at least be possible to set an upper limit to the 

 intensity of the electrical field at this level in the solar atmosphere. 

 The observations will also be extended on the laboratory side, and 

 applied to various promising regions of the solar atmosphere. 



THE FLASH SPECTRUM WITHOUT AN ECLIPSE. 



During the year an investigation was completed by Mr. Adams and 

 Miss Burwell of the chromospheric spectrum in the region X 4800 to 

 X 6600, based on photographs taken with the 60-foot tower telescope. 

 A total of 1,193 bright lines have been observed in the region X 4800 to 

 X 6600. Of these the wave-lengths of 1,024 have been measured, and 

 the remaining 169 have been noted as pairs of bright fringes on the 

 sides of absorption lines. 



A comparison with Mitchell's eclipse spectrum results indicates that 

 the number of lines is somewhat greater on the tower telescope photo- 

 graphs. Between X4800 and X5880 Mitchell gives 901 lines, while the 

 Mount Wilson negatives give 1,027. The average deviation of the 

 wave-lengths of the measured bright lines from the corresponding dark 

 lines of Rowland's table is, in the case of the Mount Wilson values, 

 0.012 a; in the case of the eclipse values, 0.030 a. For the purposes of 

 this comparison only single lines, and not blends, have been included. 



Double reversal is a universal characteristic of the stronger dark 

 lines of the solar spectrum when seen in the chromosphere. The bright 

 lines are symmetrical with reference to the dark central line in essen- 

 tially every case, and the two components in a great majority of cases 

 have equal intensities. 



A very low level in the solar atmosphere for the point of observation 

 is indicated: (a) by the double reversal of the stronger Fraunhofer 

 lines; (6) by the great number of very faint Fraunhofer lines, which 

 appear bright in the chromosphere; (c) by the great strength of the 

 carbon fluting at X 5165. 



The effect of this low level as compared with that of the eclipse 

 observations is seen in the differences among the lines observed. Most 

 of the strong Fraunhofer lines appear as single bright lines on the 

 eclipse photographs. On the tower telescope photographs some of 

 these lines appear only as dark lines, and the others are seen as double 

 reversals, or as dark lines with bright fringes. These lines belong to 

 a comparatively high level in the solar atmosphere. On the other 

 hand, the tower telescope photographs show hundreds of bright lines 

 due to very faint Fraunhofer lines, which are at a low levei in the 

 reversing layer. 



The Unes of La, Ce, and other elements of high atomic weight appear 

 as very strong bright lines in the chromospheric spectrum. At the 



