A. MATHEMATICS AND ASTRONOMY. 29 



in most of them the difficulty of attaining exact measure- 

 ments has been almost insurmountable, because of the faint- 

 ness of the objects. The spectrum of the second comet of 

 1868 seemed to Huggins to give with some certainty a coin- 

 cidence of the three bright bands with the three bands of ole- 

 fiant gas, and it has been somewhat rashly inferred that the 

 hydrocarbons were generally present in the cometary sub- 

 stance. This opinion, however, Vogel combats with consid- 

 erable force, showing that of nine comets examined within 

 ten years there is as yet only one for which two reliable ob- 

 servers agreed in asserting a probability of coincidence of 

 the lines in its spectrum with those of hydrocarbons ; and 

 Vogel thinks we should content ourselves with the deduction 

 that a portion of the light is emitted by the comet itself, very 

 probably from glowing gas, the remainder being that which 

 is reflected from the comet's surface. In regard to the vari- 

 ous statements that nitrogen, aqueous vapor, and other bodies 

 have been identified in these comets, they can not be accept- 

 ed as firmly established. These are merely hypotheses that 

 should have a stimulating influence on the progress of scien- 

 tific research. 12 A, IX., 193. 



ORIGIN OF AURORAS. 



Mr. E. B. Elliott, of the Bureau of Statistics at Washing- 

 ton, advances the theory that the exhibitions of brilliant and 

 marked auroras are connected with the rate at which the 

 earth approaches to or recedes from the sun. Pr.Am. Assoc, 

 1873. 



VOSTOKOFF ON OLBERS's METHOD OF DETERMINING THE PARA- 

 BOLIC ORBITS OF COMETS. 



A young Russian astronomer, Yostokoff*, already known in 

 his own country by several works in theoretical astronomy, 

 and who is professor of this department in the University 

 of Warsaw, has lately published a memoir on the deter- 

 mination of the parabolic orbits of comets, in which he in- 

 troduces several modifications of the method published by 

 Olbers. The formula?, as arranged by Yostokoff*, have appar- 

 ently a very considerable degree of convenience, and he has ap- 

 plied them, by way of example, to the second comet of 1813, 

 and also to the first comet of 1871. The peculiarity of his 



