Mr. W. lluggins on the Spectra of the Sun §c. 59 



is favourable for the successful prosecution of this very delicate 

 research. 



§ V. Observations of the Sun. 



The author has observed the sun with three distinct objects in 

 view : — 



1 . He has sought to discover if the spectrum of the light from 

 the less luminous part of the sun near the limb, differs in any respect 

 from that of the light from the central parts of his disk. 



2. He hoped to obtain a view of the red prominences visible 

 during a solar eclipse by reducing the light from our atmosphere by 

 dispersion; for, under these circumstances, if the red prominences 

 give a spectrum of bright lines, these lines would remain hut little 

 diminished in brightness, and might become visible. 



His observations in these two directions have been hitherto unsuc- 

 cessful. 



3. He proposed to seek to gain, from an examination of the spectra 

 of the umbrae and penumbrse of solar spots, some information as to 

 the nature of these phenomena. He has successfully applied the 

 large spectroscope, already described, to the light from the umbra of 

 a spot. 



His observations are in accordance generally with those communi- 

 cated by Mr. Lockyer to the Royal Society. 



The author describes the examination of a spot on April 15th, 

 1868. He shows that about three-fourths of the apparent light of 

 the umbra came from that region of the sun, and the remaining 

 fourth from the intervening illuminated atmosphere of the earth. 

 He observed an increase of width in most of the dark lines of the 

 solar spectrum. The lines C and F, due to hydrogen, did not ap- 

 pear stronger in the spectrum of the umbra. No new lines were 

 detected, nor were any of those of the normal solar spectrum observed 

 to be wanting, in the spectrum of the light from the umbra. No 

 bright lines were seen. 



Some of the conditions of the solar surface are considered which 

 the phenomena observed may be supposed to indicate. 



A cooler state of the heated vapours by which the lines of ab- 

 sorption are produced would diminish the radiation from the gas 

 itself, and so leave more completely uncompensated the absorption 

 by the gas of the light from behind it. Though in this way an 

 apparent increased intensity of the dark lines would result, the obser- 

 vations seem to suggest a state of the vapours, connected with ten- 

 sion and temperature, in which their power of absorption for each 

 line embraces an increased range of wave-length. Some of the con- 

 ditions under which this state of things may be brought about are 

 discussed. 



The absence of bright lines is not considered conclusive of the 

 complete absence of light in the umbra from luminous gas ; for if 

 there existed in the spot or above it the same vapours in a cooler 

 state, the light would be almost wholly absorbed, and the feebler ema- 

 nations of the cooler vapour might not do more than render less 



