120 H. Draper— Photograph of Jupiter's Spectrum. 
disk, but analyzed a band at right angles to the equator and 
extending across the disk. If either absorption or production 
of light were taking place on that portion of Jupiter’s surface 
there might be a modification in the intensity of the general 
background of the photographed spectrum. 
A casual inspection will satisfy any one that such modifica- 
tions in the intensity of the background are readily perceptible 
in the original negative. They seem to me to point out two 
things that are occurring: first, an absorption of solar light in 
the equatorial regions of the planet; and second, a production 
of intrinsic light at the same place. We can reconcile these 
apparently opposing statements by the hypothesis that the 
temperature of the incandescent substances producing light at 
the equatorial regions of Jupiter did not suffice for the emission 
of the more refrangible rays, and that there were present 
materials which absorbed those rays from the sunlight falling 
on the planet. 
If the spectrum photograph exhibited only the absorption 
phenomenon above 4, the interest attached to it would not be 
' great because a physicist will readily admit from theoretical 
considerations that such might be the case owing to the colored 
belts of the planet. But the strengthening of the spectrum 
between / and F in the portions answering to the vicinity of 
the equatorial regions of Jupiter bears so directly on the prob- 
lem of the physical condition of the planet as to incandescence 
that its importance cannot be overrated. 
he circumstances under which this photograph was taken 
were as follows: Longitude of observatory 4" 55" 29*-7 west of 
Greenwich. Night not very steady. Jupiter and the moon 
differed but little in altitude. Jupiter’s spectrum was exposed 
uous from its tint to the eye might readily modify the spectrum 
in the manner spoken of above. 
