134 DR L. BECKER ON THE SOLAR SPECTRUM. 



nearly an arithmetical progression which could easily be made perfect without moving 

 appreciably from the middle of each band. The first, third, and fifth of this series are 

 the strongest in their respective parts of the spectrum. It will be interesting to see if 

 the water-vapour bands beyond F fit into the series given above. Possibly they may 

 also give some information about the water-vapour group near B and the ctband. 1 



Outside the groups mentioned but few telluric lines have been picked out, although 

 the work has been done without knowing where telluric lines would occur. In fact, 

 previous maps were only consulted after our charts were drawn. 



We close this chapter by alluding to the faintness of the more refrangible part of the 

 spectrum in the low sun. According to our observations this dulling of the continuous 

 spectrum is independent of the intensities of the water- vapour lines between b and F, but 

 varies with the transparency of the air. We therefore conclude that its variable part is 

 produced by condensed water- vapour. 



Catalogue of Lines. 2 



The first column contains the oscillation frequencies which are identified with the 

 reciprocal values of the wave-lengths. The wave-lengths are given in the fourth column 

 in Angstrom's units, of which there are 10 millions in a millimetre. The second column 

 gives the adopted intensities of blackness of the solar and telluric lines as they would 

 appear at medium altitudes of the sun for an average amount of water-vapour (elastic force 

 of vapour = 0'5 inch). The third column shows the intensities of the telluric lines only, 

 when the sun is at an apparent altitude of 1° to 2°. Unless both components of double 

 lines were measured repeatedly, the line has been entered as single with the letter d 

 affixed to the intensity. The letter b means band. It stands either between two lines 

 which form the borders of the band or it is affixed to the intensity, in order to show that 

 the line is broader than its intensity alone would lead one to expect. The intensity of 

 the light between two lines is signified by the letter i before the figure giving the 

 intensity. Lines which have been only once observed are considered to be doubtful and 

 are marked therefore with ?, unless they are of the lowest intensity (1). The same 

 notations are employed with the telluric lines in column 3. In this column the sign ? is 

 intended to show that the telluric character of the line is open to some doubt, whereas 

 the same notation enclosed in brackets is chosen to express the bare possibility that the 

 line is telluric. 



The columns from 5 onwards comprise the original observations of intensity in full, 

 without any corrections whatever, — first those made at medium altitudes, and then those at 

 low altitudes of the sun. Each column is headed by the number of the series, which ranges 

 from 1 to 13 in high sun, and from 1 to 73 in low sun. They enable the reader to find 



1 M. Thollon'h maps, which we have just received (see Postscript), give water-vapour lines in the a-group, the middle 

 of the band being in - = 1586. Each of the first three bands of the series is thus followed by a group of lines which are 

 fainter than the bands themselves. 



2 The Catalogue begins on p. 48. 



