Royal Society. 1 39 



tute the processus cerebelli ad medullam oblongaiam. This subdivi- 

 sion of the posterior columns may be traced throughout the whole 

 length of the spinal cord. The lateral columns give origin to the pos- 

 terior roots of the spinal nerves, and are therefore the parts subser- 

 vient to sensation. In ascending towards the brain, each of these co- 

 lumns has a double termination j first, in the root of the fifth pair of 

 cephalic nerves ; and secondly, in the place where both columns unite 

 into one round cord, and mutually decussate. 



Between the lateral and the anterior columns there is interposed a 

 layer of cineritious matter, constituting a continuous stratum from the 

 cauda equina to the roots of the auditory nerves. There is also a 

 septum, dividing the right and left tracts subservient to sensation in 

 the region of the fourth ventricle, and apparently terminating at the 

 point of decussation of these tracts ; but, in reality, separating to al- 

 low of this decussation, and joining the central portion of the cord, 

 which connects the posterior with the anterior columns, and extends 

 from the pons Varolii to the cauda equina. 



The anterior columns, constituting, at their upper part, the corpora 

 pyramidalia, after their union and decussation, compose the motor 

 columns of the spinal cord. They do not, in their course, unite or 

 decussate with the lateral, or sensitive columns j decussation taking 

 place only among the columns performing similar functions; that is, 

 the motor columns with the motor, and the sensitive with the sen- 

 sitive. 



May 7. — The first paper read was entitled, " On the Elements of 

 the Orbit of the Comet of Halley in 1759." By J.W. Lubbock, Esq., 

 V.P. and Treasurer of the Royal Society. 



In calculating the elements of Halley 's comet, former astronomers 

 have in general adopted the parabolic hypothesis, neglecting the re- 

 ciprocal of the semi-axis major ; and even in the more recent inves- 

 tigations of its orbit, no accurate value of this quantity has been em- 

 ployed. Mr. Lubbock, perceiving the serious effect which an error in 

 the semi-axis major would occasion in the determination of the other 

 elements, renewed these very laborious calculations, assuming as the 

 value of this quantity that given by M. Ponteeoulant, in his "Theorie 

 analytique du Syst6me du Monde ;" taking also into account the al- 

 terations which the elements of the comet have undergone by the 

 action of the planets, and likewise the effect of precession upon the 

 longitude of the node, and of the perihelion. The author takes this 

 opportunity of correcting the very erroneous statements that have 

 been made respecting the results of his investigations, especially with 

 regard to the time of the perihelion passage, which is, of course, very 

 different from that of its actual appearance to spectators on the 

 earth j although these two epochs are frequently confounded with one 

 another. 



The second was entitled, " Formulae for computing the Longitude 

 at Sea; " by William Dunlop, Esq. Communicated by the Secretaries. 



These formulae, in which the longitude and latitude of two points 

 in a spherical surface, together with the arc of the great circle inter- 

 cepted between them, are supposed to be given, furnish the means 



T2 



