January 21, 1898.] 



SCIENCE. 



101 



At a certain height above the photosphere the 

 chromosphere spectrum in a photograph of the 

 chromosphere visible at any one instant beyond 

 the edge of the moon will show arcs of certain 

 relative intensities. As the moon advances and 

 gradually uncovers the base of the chromo- 

 sphere the same arcs will remain visible, but 

 those produced by a layer which does not ex- 

 tend down will be reduced in intensity as com- 

 pared with arcs produced by vapors which do 

 reach lower down ; the latter will continue to 

 get brighter, while the others remain at the 

 same absolute intensity. As the lowest part of 

 the chromosphere is shown in the photographs 

 taken immediately after totality, or exactly at 

 the end, it is only necessary to compare the 

 relative intensities of the arcs in different pho- 

 tographs, in order to investigate the general 

 question as to the existence of layers." 



Let us now consider what we should be led to 

 expect under the hypothesis that all the gas- 

 eous envelopes rest upon the photosphere. 

 There are no grounds for believing that those 



the chromosphere, and the abscissae the bright- 

 ness of a gas at that point. The lines a, b, c 

 and d are supposed to represent the relation 

 between "height and brightness of four different 

 gases. For simplicity, and in the absence of 

 definite information upon the subject, these 

 lines are assumed to be straight. If the exami- 

 nation is made close to the photosphere the 

 effective intensity of the arc will be proportional 

 to the amount of gas uncovered per unit of 

 length along the moon's edge. Fig. 2 has been 

 roughly sketched to indicate the effective in- 

 tensity at different levels. Fig. 3 shows the 



-> 3 



Fig. 1. 



gases which extend the highest should be in- 

 trinsically the brightest. In fact, we should ex- 

 pect extent and brightness to depend largely 

 ujion separate conditions. In Fig. 1 let the 

 ordinates represent the height of a point above 



Fig. 3. 



relative intensities of the lines at the levels in- 

 dicated. If the extent of some of the vapors is 

 so great that their arcs have a considerable area 

 the case is still further complicated. If we un- 

 derstand our author aright, a series of photo- 

 graphs corresponding to Fig. 3 would indicate 

 layers d and b resting on the photosphere, fol- 

 lowed by c higher up and finally by a alone. 

 It is true that a rough scale of absolute bright- 

 nesses might be built up by comparing the mid- 

 dle of the arc with portions nearer the cusps, 

 but such an arrangement would be only approx- 

 imate, and is evidently not intended by the 

 author. It is not, therefore, 'at once apparent 

 that the riddle proposed by the relative inten- 

 sities of a large number of lines belonging to 

 different gases is easy of solution. 



It is with regret that the reader finds through- 

 out the work statements and suggestions to 

 which, perhaps, for a want of comprehension 

 of exactly what is meant, he is forced to issue a 



