164 PROCEEDINGS OP THE ACADEMY OF 



Ferent constitution of its surface. The Greek astronomers were acquainted 

 with red stars only, while modern science has discovered, by the aid of the 

 telescope, in the radiant fields of the starry heavens, as in the blossoms of 

 flowering plants and in the metallic colors, almost all the gradations of the 

 prismatic spectrum." The turn of the expression "still less " shows that he 

 regarded the matter as inconspicuous and unimportant, and the remark is 

 made only in a casual manner. Nevertheless, incidental as the remark may 

 seem, it is the most precise and circumstantial I have found in any author on 

 the influence of the atmosphere on the colors of the stars. But is it really 

 true that the atmosphere can impart a transient and generally red color to 

 stellar light when near the horizon ? In the absence of all confirmation to 

 the above remark of the distinguished philosopher, I selected as test stars 

 Vega and Capella, both first magnitude stars, the former green and the latter 

 blue, and the one or the other is grazing the northern horizon nearly all the 

 year. But I have been unable to detect the changes he mentions. May not 

 his remark have arisen from observations on the planetary bodies, and have 

 been inadvertently extended to the fixed stars? The planets, especially Ju- 

 piter, according to my observations, are sometimes, though rarely, sensibly 

 reddened like the sun and moon by the atmosphere. But whether Humboldt's 

 assertion be confirmed or not, it cannot effect our decision about the real 

 changes of the colors of the stars. No one would pretend to announce a 

 change in the color of a star simply because of a " transient " appearance of 

 a change while near the horizon. In the same manner, probably, the idea 

 has got afloat in a vague manner that, because the atmosphere of our earth 

 has the capability of giving occasionally a red color to the sun, moon and the 

 planets, it must therefore have not only the same effect on the fixed stars, but 

 even the power to turn them to all the hues of the spectrum between red and 

 blue. But this rapid generalization is no more warranted by sound reason- 

 ing than by observation. The sun, the moon and the planets have sensible 

 disks, which the fixed stars have not. Hence the optical phenomena of these 

 two classes of bodies differ widely. The fixed stars, under the influence of 

 our atmosphere, are made to scintillate ; they then twinkle with an unsteady 

 light, and to good eyes they flash out rapidly and fitfully all the varieties of 

 colors. This shows the difference, in an optical point of view, between the 

 fixed stars and the other celestial bodies, and the impropriety of a hasty gene- 

 ralization from one class to the other. Because the atmosphere can redden 

 one class it by no means follows that it can redden the other, much less that 

 it can impart to the other all imaginable hues. 



Another cause for the belief that the atmosphere can impart different colors 

 to the stars, may be found in the necessity for some explanation of their 

 changes of color. It is assumed, though without any known reason, that the 

 intrinsic colors of the stars cannot change, at least in the space of two thou- 

 sand years, and hence there is a necessity for an explanation of their appa- 

 rent changes in some other way ; and as the handiest method these changes 

 are attributed to the atmosphere of our earth. That the various colors of the 

 stars are not produced by our atmosphere, nor by optical instruments, nor by 

 personal peculiarities of vision, becomes perfectly evident from the following 

 simple consideration. If their colors were produced by any one of these 

 causes, then there would not be that beautiful contrast of colors which we 

 now behold; then it could never have been said of the cluster Kappa Crucis, 

 that the various bright contrasted colors of its different members give it all 

 "the effect of a superb piece of fancy jewelry." Instead of this there would 

 be in that cluster, and in every other region, a dull monotonous color in all 

 the stars alike. It has happened that travellers, in coming from Europe to 

 America, have expressed their surprise at the beauty of our sky, when notic- 

 ing for the first time in their lives the different colors of the stars. This hag 

 been supposed to be the work of our atmosphere, the natural operation of the 



[June, 



