100 
LUMMER. 
Its most striking consequence was that the bright lines of 
the chromosphere may appear doubled, since local decreases 
of density from exterior parts to central parts of the sun may 
also occur. Indeed, every photograph taken by the Dutch 
expedition to Sumatra in 1901, on the occasion of the sun’s 
eclipse, showed a doubling of all chromosphere lines. Hart- 
mann, of Potsdam, however, believes that the doubling of 
the lines is produced by errors of the apparatus. 
Finally, when an observer looks at only the parts between 
aa and bb (or a x a x and b x b x ) of the whole phenomenon 
(Fig. 7) he observes only two broad bright bands of light, 
the position of which is different from that of the D lines. 
Earlier theory assumed this deviation to be produced by the 
Doppler principle, by supposing gas eruptions with a velocity 
of 500 kilometers per second. These enormous velocities 
astonished all astrophysicists, but they were finally believed, 
since no other explanation existed. 
If these enormous velocities are due to a sudden rise of 
temperature, calculations based on gas theory show that a 
temperature of five million degrees would be necessary to 
impart to the molecules of hydrogen a velocity of only 200 
kilometers per second. Anomalous dispersion gives an ex- 
planation of the observed displacements without any re- 
strictions. 
The phenomenon most difficult of explanation of all 
observed since the spectroscope was invented is the following: 
In the spectrum of one and the same prominence, or at one 
and the same place near a sun-spot, the bright lines of one 
element show distortion, while those of another element are 
fairly straight, and it is most astonishing that even the dif- 
ferent lines of one and the same element show a quite differ- 
ent appearance (Fig. 9). Some are deviated and curved, 
others are in their proper place and are straight lines. 
In order to explain this curious fact, Sir N. Lockyer in- 
troduced the hypothesis that on our sun the elements are 
dissociated into elementary atoms. This idea sounded at 
that time somewhat ridiculous; but now, after the discovery 
of radium and the transformation of its emanation into 
helium, etc,, we must admire Lockyer’s imagination and 
