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SIE DAVID BEEWSTEE AJsD DE. J. H. GLADSTOAT: OX 
1st. That the light when emitted from the photosphere itself is deficient in these rays. 
This was evidently the idea of Feauxhofer. 
2nd. That they are due to absorption by the sun’s atmosphere. 
3rd. That they are due to absorption by the earth’s atmosphere. 
Or it is conceivable that some of these lines and bands have one origin and some 
another, though it seems more natural to refer them all to one cause. 
The first supposition, that they are originally wanting in the hght itself, scarcely 
admits of a positive proof. 
If the second supposition, that they (or some of them) are due to the sun’s atmosphere, 
be true, it may be expected that the light which comes through a minimum amount of 
such atmosphere would present less appearance of these lines than that which has 
traversed a longer portion. During the eclipse of the sun in March 1858, Dr. Glad- 
stone made preparations for determining whether the light coming merely from the thin 
edge of his disk would be difierent in this respect from the ordinaiy sunlight, but unfor- 
tunately clouds prevented the experiment being carried out on that occasion*. How- 
ever, by other contrivances, each of the authors came independently to the conclusion 
that there is no perceptible difierence in this respect between the light from the edge 
and that from the centre of the solar disk. 
That the earth’s atmosphere has much to do with the manifestation of these lines is 
beyond all question, and the analogy of such gases as nitrous acid, or bromine vapour, 
suggests the idea that they may originate wholly in the air that encircles our globe. Xor 
does the observation that an increased depth of air affects some lines greatly, and others 
little, if at all, militate against the supposition that they are all due to the same 
absorbent medium ; for such a band as No. 44 of the nitrous acid spectrum (fig. 10) Avill 
appear much the same whether a thin or a thick stratum of the gas has been interposed, 
while the band No. 10 will only make its appearance when the stratum is deep. Again, 
a thin stratum of a uranium salt in solution shows a dailc band in the greenish-blue 
space, and on increasing the thickness this dark band remains almost the same in uidth. 
while four new bands make their appearance in the blue portion, and the riolet is 
absorbed. This question, however, appears susceptible of an exjjenmentum cruci^. 
Were we to take any artificial light, and examine it by a prism through a sufficient 
length of air, we ought to see the fixed lines developing themselves, if they be due to 
the atmosphere, or entirely absent, if otherwise. This wms tried by Dr. Gladstone. 
The lighthouse at Beachy Head exhibits tliirty oil-lamps on a triangular stage, each 
furnished with a large parabolic silvered reflector. The light of ten of these lamps at 
once is thus thrown into one beam, which as the apparatus revolves sweeps the horizon, 
and is visible about as far as any artificial light in existence. On the nights of August 
* After this communication had been sent to the Society, Dr. Gladstone vas made acquainted with the 
fact that the same idea had occurred previoxisly to Professor Eoebes, and that he had determined by the 
annular eclipse of May 15, 1836, that the light from the edge of the solar disk is identical in this respect 
with ordinary sunlight. — Phil. Mag. vol. ix. p. 522. 
