162 PROCEEDINGS OF THE ACADEMY OF 



method of investigation and the results to which I have been led. To ascertain 

 what the influence of the atmosphere might be, I selected for special obser- 

 vation a few of the larger stars, taking some of the red, some of the blue, 

 some of the green, some of the yellow, and some of the white. So many 

 different classes of stars watched carefully during the various changing con- 

 ditions of the atmosphere, seemed most likely to yield valuable conclusions. 



1. The red stars were Aldebaran, Antares, and Betelgeuse. These are all 

 of different shades and intensities of red. In proportion as the atmosphere 

 loses its transparency by the condensation of moisture, these stars lose their 

 distinctive peculiarities. Their redness gradually becomes obscured, and they 

 at last appear of a dull, unsatisfactory white. 



2. The blue stars were Capella, Rigel, Bellatrix, Procyon and Spica. Some 

 of these, as first Procyon, and then Rigel, are far more intensely blue than 

 the others. But as the atmosphere becomes thick and more impervious to 

 distinct vision, their different intensities of blue fade away, and the observer 

 is at length puzzled to decide of what color these stars really are. He feels 

 safest in announcing that they seem white, though not of a clear, decided 

 whiteness. 



3. The green stars were Sirius, Vega, Altair and Deneb, or the largest star 

 in the Swan. These stars were observed to be green by myself, in the fol- 

 lowing order: Sirius in the autumn of 1862, Vega in June, 1863, and Altair 

 and Deneb in August, 1863. It is remarkable that a very slight haziness in 

 the sky completely hides their green color, and causes them to appear un- 

 mistakably blue. A still thicker haziness has the same effect on them as it 

 has on all the blue stars already described, gradually obscuring their blue 

 color, and ranking them among the many hundreds of stars which the naked 

 eye cannot decide to be colored. 



4. The yellow star was Arcturus ; this being the only one which appears 

 decidedly yellow to my vision, unaided by instruments. Several others in- 

 cline the naked eye to regard them as yellow, such as Polaris and the larger 

 stars of Ursa Major and of Cassiopeia, but not sufficiently so to produce a 

 firm belief. Arcturu3, in a clear sky, has a fine light orange yellow ; but ag 

 the sky becomes less and less clear, the yellow fades away, and ultimately 

 the color of this star turns to a dim white, and becomes undistinguishable 

 from that of the larger stars of Ursa Major, with which, from their position, 

 it may be handily compared. 



5. The white stars were Regulus, Denebola, Fomalhaut, Polaris, the con- 

 stellation of the Wagon, and several others of the second and third magni- 

 tudes. They may be called white stars with reference to their appearance to 

 the naked eye, to mine at least, but we are not bound on that account to 

 believe them to be really white. As they are not first magnitude stars, they 

 probably seem white to the unaided eye only because their light is not suffi- 

 ciently great in amount, or intense in color, to appear colored. There may 

 be persons with unaided vision acute enough to perceive their true colors. 

 But whatever may have been the conditions of the atmosphere, I have never 

 observed them to be other than white. No changes of the air have had the 

 power of presenting them in any shade as colored stars. 



Thus the influence of the atmosphere of our earth upon the stars of all the 

 different colors, according to these observations, is the same. Whether the 

 stars be red, blue, green or yellow, the effect of changes in the atmosphere is 

 to rob them of their peculiar shades and intensities, and to reduce them all 

 to a dull colorless condition, — a dim whiteness, in which their indistinctness 

 produces a feeling of uncertainty and doubt in the beholder. Nor in any case 

 have I seen any change in the atmosphere turn a star from one color to 

 another, except from green to blue, and this is simply reducing one shade to 

 another; for green, like purple, is but one of the modifications of blue. I 

 have never seen a red star become blue, nor a blue star become yellow, nor 



[June, 



