Intelligence and Miscellaneous Articles. 77 



These three groups all present the same aspect : they consist of a 

 very marked line, and of a series of very fine ones, almost equally 

 distant ; the intensity alone increases in going from C towards A. 

 The constant appearance of these three groups, and their similarity 

 of aspect, lead us to attribute them to a common origin; but, as I 

 have said, this is not to be sought in the action of aqueous vapour, 

 but rather in that of a permanent gas, carbonic acid for instance. 



The spectra of the compound gases, and more especially those of 

 metallic oxides, present great similarity to the groups in question ; 

 and this leads me to suppose that they are due to the absorption 

 exerted by a compound gas. That they belong to our atmosphere, 

 and not to that of the sun, follows from the change of intensity of 

 B, and especially of C, with the height of the sun, and also from 

 their general appearance ; for they have not, like all others which 

 possess a certain intensity, a direct relation with the spectrum of a 

 simple body. 



The hypothesis of the solar origin of Fraunhofer's lines has this 

 consequence, that the spectrum formed by rays emanating from the 

 edge of the star ought to show these lines more strongly than does 

 the spectrum of the rays from the centre. Yet this prevision of the 

 theory is not confirmed ; at all events the result has not corre- 

 sponded to the expectation of physicists. The experiments of 

 Mr. Forbes and myself have given a negative result. Yet a differ- 

 ence has been established ; the light in the centre has only furnished 

 in the middle of the spectrum the strongest of Fraunhofer's lines, 

 but with a very pronounced intensity : the contrary would have been 

 expected. 



In the course of last year, in common with M. Thalen, I under- 

 took a comparison of the solar spectrum with that given by the iron 

 electrodes of a battery of 50 elements. We discovered more than 

 460 lines corresponding to the iron lines. These experiments led 

 me to view the phenomena of absorption under a new point of view, 

 which ought, I think, to dispel the contradiction which I have indi- 

 cated between theory and observation. 



If, for instance, we observe the iron lines by the aid of a powerful 

 RuhmkorfT's coil, three very brilliant and some other feebler lines 

 are observed between Gr and the strongest calcium lines. But 

 if the inductorium is replaced by a battery of fifty elements, not only 

 does the number of lines very materially increase, but their relative 

 intensity undergoes great changes. Among the fifty lines which 

 we then counted in this limited region of the spectrum, we could 

 only with difficulty identify the three intense lines observed with 

 the inductorium. 



Applying this result to the sun, we may suppose that the rays on 

 the edge will not give a spectrum in which the most intense rays will 

 have a relatively greater intensity, but a spectrum in which, on the 

 contrary, the feeblest will be the most pronounced ; the result will 

 be a feebler spectrum — that is, one without very pronounced rays. 

 This is exactly what I have observed, although the difference of the 

 two spectra be not considerable. It is easy to produce in the solar 

 spectrum changes which have been ascertained in the iron spectrum. 



