NATURAL SCIENCES OF PHILADELPHIA. 57 



prepossessions in the case, they should be that the changes are real in the stars 

 themselves. And when we reflect on the habitual caution of long experienced 

 observers, men whose very existence is devoted to the accurate delineation 

 of fact, we should place a high reliance on their recorded observations, and 

 not think that they have lightly allowed themselves to be imposed upon by 

 optical illusions. 



I cannot hope to be able to add anything to the knowledge of practised ob- 

 servers respecting the sources of error and the rules to be observed in making 

 observations ; but as these have never, that I am aware, been embodied in 

 print, I offer the following, chiefly for the assistance of the many who may 

 be disposed so observe the larger stars with the naked eyes. Such stars are 

 indeed very few, but the observations may be the more useful from being made 

 frequently and by many persons. 



1. Damp and slightly hazy atmospheres make a green star appear blue. 

 This may be from the same principle that the deep ocean, the clear sky, and 

 the distant mountains appear blue. Damp nights that are perfectly clear do 

 not have this effect. 



2. Moonlight greatly obscures the colors of the stars, giving them a yellowish 

 hue. 



3. Before the daybreak makes its appearance in the east, the rays of the sun 

 refracted through the higher regions of the atmosphere, may cause a general 

 whiteness of the stars. 



4. Artificial lights reaching the eye obscure the colors of the stars. 



5. On account of the faintness of the light of the stars, the eye of.en requires 

 to be fixed upon them for a considerable time before their impressions take 

 full effect. 



6. Comparisons between neighboring stars, and some practice in star ob- 

 servations, are often necessary to decide on the real colors of the stars. 



7. The atmosphere must have like effects upon similar stars in the same 

 neighborhood. Hence a peculiarity observed in any star may be brought to a 

 determination. 



8. Observations on the same star during a considerable interval of time and 

 through different changes of weather, may aid in giving confidence to a deter- 

 mination. 



9. Perfect independence and candor are necessary. Our previous judgments 

 are apt to warp these dalioate impressions on the retina, and whether we have 

 derived these judgments from ourselves or others, we must be careful to lay 

 them completely aside. For want of doing this we may not notice a change of 

 color, although such a change may have been before our vision. 



10. Personal peculiarities of vision may be ascertained by consultation with 

 others. 



11. Discrepancies between the accounts of two observers may arise from 

 differences of dates ; hence, in apprehension of sudden and frequent changes in 

 the stars, the dates of observations should be carefully given. m 



Description of a new Labroid Genus allied to TROCHOCOPUS Gthr. 



BY THEODORE GILL. 



Dr. Ayres bas indicated, under the name Labrus pulcher, a Californian 

 representative of the family of Labroids. That species was subsequently 

 referred by Dr. Glinther to his genus Stinicossyphus, in which it was retained 

 by myself with the proviso that " its generic position remains to be con- 

 firmed, although there is little doubt that it really is a Semicossyphus." Hav- 

 ing since received, through the kindness of Dr. Cooper, a specimen of the 

 species, I find that it has not the "lateral teeth distinct," as in Semicossyphus, 

 but an " obtuse osseous ridge round the edge of the jaws, without distinct 

 lateral teeth," as in Trochocopus Gthr., to which Gunther should have referred 

 it. I am not acquainted with his reasons for considering the species closely 



1864.] 



