424 
ME. W. HUGGINS AND DE. W. A. MILLEE ON 
The imperfect evidence which analysis by the prism affords of the existence of atmo- 
spheres around these planets, notwithstanding the high probability, amounting almost 
to certainty in the case of Jupiter, that such atmospheres do exist, may receive an ex- 
planation in the supposition that the light is chiefly reflected, not from the planetary 
surfaces, but from masses of cloud in the upper strata of their atmospheres. In this 
case the length of atmosphere which the light would have to traverse would be con- 
siderably lessened. With perhaps the exception of Mars, telescopic observations are in 
favour of such a supposition. 
§ IV. Observations on the Fixed Stars. 
10. The number of fixed stars which we have, to a greater or less extent, examined 
amounts to nearly 50. We have, however, concentrated our efforts upon three or four 
of the brighter stars, and two only of these have been mapped with any degree of com- 
pleteness. These spectra are, indeed, as rich in lines as that of the sun, and even with 
these it may be advantageous to compare the spectra of additional metals when the season 
is again favourable. The few really fine nights that are available whilst the star is well 
situated for such observations, in respect of altitude and the time of sun-setting, neces- 
sarily make the complete investigation even of a single star the work of some years. 
11. Aldebaran (a Tauri) (Plate XI.). — The light of this star is of a pale red. When 
viewed in the spectroscope, numerous strong lines are at once evident, particularly in 
the orange, the green, and the blue portions. The positions of about seventy of these 
lines have been measured, and their places have been given in the Table. Besides these, 
numerous other strong lines are visible, particularly in the blue, but they have not been 
measured, owing to the feebleness of the light ; we have therefore not inserted them in 
the Table or in the diagram. A similar remark is applicable also to the results of our 
examination of a Orionis and (3 Pegasi. 
We have compared the spectra of sixteen of the terrestrial elements by simultaneous 
observation with the spectrum of Aldebaran, of course selecting those in which we had 
reason, from the observations, to believe coincidence was most likely to occur. Nine of 
these spectra exhibited lines coincident with certain lines in the spectrum of the star. 
They are as follows : — sodium, magnesium, hydrogen, calcium, iron, bismuth, tellurium, 
antimony, and mercury. 
(1 ) Sodium. — The double line at D was coincident with a double line in the stellar 
spectrum. 
(2) Magnesium. — The three components of the group at b, from electrodes of the 
metal, were coincident with three lines in the star-spectrum. 
(3) Hydrogen. — The line in the red corresponding to C, and the line in the green cor- 
responding to F in the solar spectrum, were coincident with strong lines in the spectrum 
of Aldebaran. 
(4) Calcium. — Electrodes of the metal were used ; four lines in its spectrum were 
observed to coincide with four of the stellar lines. 
