A. MATHEMATICS AND ASTRONOMY. 51 



able, yet their eifect ^dll disappear, in great part, on taking 

 the mean of each pair of corresponding contacts. It remains 

 then to determine the coefficients necessary in order to re- 

 duce the apparent moment of contact of the limbs of the 

 planets and satellites to the true moment of the contact of 

 the centres of these planets. Bull. Imp. Acad, of S>ciences^ 

 St. Petersburg^ vol. xviii., p. 98. 



ox THE EXISTENCE OF A RESISTING MEDIUM IN SPACE, 



It is well known that the principal argument in support 

 of the existence of a gaseous medium in space, that offers 

 sensible resistance to the motions of bodies through it, is 

 drawn from tlie computations of Encke, in reference to the 

 comet commonly known as Encke's comet. The observa- 

 tions of the successive appearances of this comet, at intervals 

 of six years between the dates of 1819 and 1848, were discuss- 

 ed by Encke with an immense outlay of*time consumed in 

 the necessary computations; and, after having made allow- 

 ance for the disturbance of the orbit of the comet by the at- 

 tractive influences of all the known planets, Encke found him- 

 self forced to conclude that the observed appearances could 

 not be reconciled with the present constitution of the solar 

 system, unless there were introduced a hypothesis as to the 

 actual existence of some gas that should retard the motion 

 of the comet around the sun. The only source of error that 

 can possibly be attributed to Encke's computations lies in the 

 intrinsic imperfections of our knowledge of the masses of the 

 planets and of the mathematical formulae employed by him. 

 In order to remove all doubt as to this question. Dr. Von 

 Asten has undertaken to go over the principal portion of 

 Encke's computations, pursuing, however, an entirely inde- 

 pendent method, and introducing the use of mathematical 

 formulae of a far more perfect nature than those emj^loyed by 

 Encke. It is only after Encke's methods of computing the 

 perturbations have been controlled by other methods whose 

 perfection is undoubted that one can decide whether the hy- 

 pothesis of the opposing medium in space is entirely untena- 

 able, or whether it merely needs slight modifications. Dr. 

 Von Asten has, in this revision of Encke's results, happily 

 availed himself of the mathematical memoirs of Gylden and 

 Hansen. The former astronomer has developed improve- 



