416 



Mr. J. N. Lockyer's Spectroscojric [Apr. 29, 



show that the absorbing material moves upwards and downwards as 

 regards the radiating material, and that these motions may be deter- 

 mined with considerable accuracy. 



IV. The bright lines observable in the ordinary spectrum are sometimes 

 interrupted by the spot-spectrum, i. e. they are only visible in those 

 parts of the solar spectrum near, and away from, spots. 



V. The C and F lines vary excessively in thickness over and near a spot, 

 and on the 11th in the deeper portion of the spot they were much 

 thicker than usual. 



IV. Stars, in the spectrum of which the absorption-lines of hydrogen 

 are absent, may either have their chromospheric light radiated from 

 beyond the limb just balanced by the light absorbed by the chro- 

 mosphere on the disk, or they may come under the condition referred 

 to in (II.), either absolutely or on the average. 



Addendum. — Received April 29, 1869. 



Since the date on which the foregoing paper was written, I have ob- 

 tained additional evidence on the points referred to. I beg therefore to be 

 permitted to make the following additions to it. 



The possibility of our being able to determine the velocity of movements 

 of uprush and downrush taking place in the chromosphere depends upon 

 the alterations of wave-length observed. 



It is clear therefore that a mere uprush or downrush at the sun's limb 

 will not affect the wave-length, but that if we have at the limb cyclones, 

 or backward or forward movements, the wave-length will be altered ; so 

 that we may have : — 



1. An alteration of wave-length near the centre of the disk caused by 

 upward or downward movements. 



2. An alteration of wave-length close to the limb, caused by backward 

 or forward movements. 



If the hydrogen-lines were invariably observed to broaden out on both 

 sides, the idea of movement would require to be received with great 

 caution ; we might be in presence of phenomena due to greater pressure, 

 both when the lines observed are bright or black upon the sun ; but when 

 they widen out sometimes on one side, sometimes on the other, and some- 

 times on both, this explanation appears to be untenable, as Dr. Frankland 

 and myself in our researches at the College of Chemistry have never failed 

 to observe a widening out on both sides the F line when the pressure of 

 the gas has been increased. 



On the 21st I was enabled to extend my former observations. 



On that day the spot, observations of which form the subject of the 

 paper, was very near the limb ; as this was the first opportunity of 



