MODERN THEORIES OF THE SUN—BOSLER. 155 
phenomenon of anomalous dispersion,’ which accounts also for the 
winged appearance of their edges (Julius). This same theory offers 
also an explanation of the divers aspects of the chromosphere, the 
flocculi, the prominences, as well as, though less satisfactorily, the 
spots. 
All that is very ingenious. Unfortunately this explanation of the 
photosphere assumes that there is no absorption of light in the sun. 
Further, the lines of the spectrum produced by anomalous dispersion 
should be unsymmetrical, and theyare not. Although somephysicists 
remain faithful to these new theories resting on anomalous dispersion, 
fascinated by their elegance, astronomers who actually see the sun 
_ Observer, 
A 
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Central | 
Regions 
Fie. 1. Fia. 2. Fig. 3. 
and observe the effects due to perspective can not believe in such a 
great optical delusion. They therefore generally cling to those ideas 
which were held in the first place and which have become classical. 
SOLAR HEAT. 
Our ideas as to the temperature of the sun remained for a long 
while in an unsatisfactory state until science made the decisive step 
which was to insure a good solution. We can not tell the temperature 
of a body at a distance except by means of some hypothesis as to 
the emissive power of its surface. But we may agree to call the 
effective temperature of a distant body that of a “black body” 
having by definition a maximum emissive and absorbing power at 
all temperatures and which, if situated at the same place, would send 
us the same amount of heat. 
The theoretical and experimental study of ‘black bodies” has 
shown that their radiation is proportional to the fourth power of 
their absolute temperature (Stefan’s law). This leads us to measure 
the amount of heat per unit time and unit surface which the sun 
sends us—that is, the ‘‘ solar constant.’’ It is about 2 small calories 
1 Wecan not here enter much into details, for which we must refer thereader to special treatiseson thesun. 
