40 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



rations of this object, he hopes to deduce something definite 

 in reference to the peculiarities of its orbit. It is well known 

 that Encke himself believed this comet to be gradually draw- 

 ing nearer to the sun, in consequence of the resistance offer- 

 ed to its movements by the a3ther existing throughout space. 

 Van Asten, however, states that his investigations have led 

 him to the surprising result that the observations of 1S65 to 

 1871 can be perfectly accounted for by the general laws of 

 mechanics, quite without calling to our assistance the attrac- 

 tions of unknown bodies or the resistance of an unknown 

 sether. If, under this assumption, we reverse the problem, 

 and attempt to deduce the movements of Jupiter from ob- 

 servations of Eneke's comet, we arrive at a result quite 

 identical with that deduced by Bessel, Kruger, and Moller, 

 so that we may be certain that the mean motion of the com- 

 et, at the time of its perihelion passage in 1868, experienced 

 not the slightest trace of an acceleration. The assumption 

 that it did experience such an acceleration, even the one-twen- 

 tieth part of that supposed to exist by Encke, leads to very 

 improbable errors. Van Asten lays stress upon the date, 

 1808, and says that while at present the comet's motions are 

 fully explicable, yet, if we extend our researches backward, it 

 does seem highly probable that at its perihelion passages in 

 1858, 1802, and 1865 the comet did successively experience 

 accelerations nearly agreeing with Eneke's suppositions. The 

 conclusion, therefore, seems reasonable that the most remark- 

 able feature of this phenomenon is the complete absence of 

 any acceleration at the perihelion passage of 1 SOS; nor can 

 this be explained on the supposition that the disturbing in- 

 fluence of the planet Mercury has been different from that 

 assumed in the calculations. As there can be no doubt that 

 the comet experiences an extraordinary perturbation in the 

 immediate neighborhood of its perihelion, Van Asten ex- 

 plains that he has, for simplicity, made the preliminary as- 

 sumption that this acceleration took place suddenly at that 

 time ; an hypothesis, however, which is not materially differ- 

 ent from Eneke's assumption that the comet moves in a re- 

 sisting medium, whose density varies inversely as the square 

 of the distance from the sun ; for, if its density vary ac- 

 cording to this law, its effect upon the comet would be main- 

 ly felt during twenty-five days before and after the perihel- 





