a Resisting Medium in Space. 405 
the introduction of forces acting in various directions, and pro- 
ducing anomalous changes in all the other elements of the 
orbit, contrary to what was required by the observations. 
cke therefore, notwithstanding the doubts of Bessel and 
other astronomers, continued steadfast in his theory of a. resist- 
‘Ing medium in space, and for more than forty years, and until 
within a short time before his death in 1865, pursued his cal- 
culations with wonderful zealand industry. Between the years 
1829 and 1859, he published in the volumes of the Berlin 
| Academy eight memoirs on the orbit of this comet, and also 
| Other investigations on the same subject in the Astronomische 
q Nachrichten and in the Berlin Jahrbuch. He assures us, what 
| We car easily believe, that he spared no labor and despised no 
| Precaution that could give completeness and surety to his com- 
ana and besides being an excellent mathematician, 
Kncke ssed, in a degree rarely equaled, the skill of ada 
ing formule to convenient and safe forms for numerical calcula- 
ions. He has given in the Berlin Jahrbuch for 1861 a résumé 
of his labors, and the proofs presented there, taken simply by 
: themselves, seem to put beyond the shadow of a doubt two 
_ Conclusions: first, that the periodic time of this comet is 
_ “minishing ; and secondly, that this diminution is satisfactorily 
_ *ceounted for by the assumption of a resisting medium in 
sh that the comet can approach very near to Mercury, so 
as the small mass of this planet, 
the perturbations which it may produce in the motion of the 
