8 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



a resisting medium in space. In this he referred to the op- 

 portunities offered by the return of Encke's comet, during 

 the present year, for determining the accuracy of Professor 

 Encke's views as to the causes of the successive retardation 

 of the periods of this comet. It may be known to some of 

 our readers that in comparing the observations of 1&10 upon 

 this comet with those of 1786, 1795, and 1805, the periodic 

 times were found to be diminished by an appreciable fraction 

 of a day ; this being due, as supposed, to the existence of a 

 resisting medium in space, assuming the fact of retardation 

 to be established. Professor Hall now thinks it likely that 

 an error may have been made by Encke in his computations, 

 especially as corrections in the calculation respecting Faye's 

 comet, supposed to be subjected to a similar retardation, as 

 the observations lately made by Professor Moller prove, are 

 satisfied within the limits of their probable error by a strict 

 adherence to the law of gravitation, and without any extra- 

 ordinary hypothesis. At the present time, then, it is only the 

 Encke comet of which the movements are in doubt. Indeed, 

 as far as the motions of comets have been determined, the ev- 

 idence, according to Professor Hall, is against the theory of a 

 resisting medium in space ; and he sums up the w T hole case 

 by saying that thus far observations of the planets lead to 

 the conclusion that their motions are in strict accordance 

 with the law of gravitation, and that it is quite possible that 

 Encke's comet, when its movements are properly understood, 

 will be found to be no exception to these conclusions. 4 Z>, 

 December, 1 871, 408. 



SPECTROSCOPICAL PHENOMENA OF ARGUS. 



Not long since, Lesueur, in applying the spectroscope to 

 the great telescope at Melbourne, ascertained the existence 

 of light lines in the spectrum of Argus, one of which was 

 probably identical with C, and the other w T ith F, and the 

 third with a light nitrogen line, while a yellow line near D 

 remains to be determined more positively. The presence of 

 hydrogen can thus scarcely be doubted, while the occurrence 

 of nitrogen, magnesium, and sodium is rendered at least prob- 

 able. 7 C, 1871,620. 



