Lowrie.] 



220 



[Nov. 19, 



III. Comets lolhose Perihelion Distances are Greater than 0.05 and Less 



than 0.1. 



Witli greater perihelion distances the tendency of the perihelia to crowd 

 together around the point indicated is less distinctly marked. 



8. Few comets of small perihelion distance should have their perihelia 

 in the vicinity of longitude 80°, the point opposite that towards which 

 the sun is moving. Accordingly we find, by examining a table of com- 

 etary elements, that with a perihelion distance less than 0.1, there is not 

 a, single perihelion between 35° and 125°; between 0.1 and 0.2, but 3; 

 and between 0.2 and 0.3 only 1. 



Bloojiington, Indiana, September litJi, 1869. 



A SEARCH FOR A NORMAL CAUSE OF THE RECESSION OF 

 COSMICAL NODES. 



By Hon. Walter H. Lowrie. 



Bead before the American Philosophical Society, Nov. 19, 1869. 



The analogy between the recession of the nodes of all the planets and 

 satellites of the solar system, including that of the earth, called the pre- 

 cession of the equinoxes, is so comj)lete and manifest that the mind, on 

 the discovery of it, naturally inclines to attribute them all to like causes. 

 These phenomena have not been so treated heretofore, but have been re- 

 garded as disturbances produced by various causes, the influence of which 

 I do not feel entitled to question, while I think there is a normal cause 

 which ought to be considered. 



It seems to me to be a proposition of axiomatic plainness, that, in any 

 system or sub-system of moving bodies, all its periodic motions ought 

 to be presumed normal, rather than abnormal, that is, the caused of them 

 ought to be first sought in the plan of the system itself ; and only when 

 this search fails ought we to suspect them to be disturbances caused by 

 forces which are alien to the system. Thus, all the periodic motions of 

 the planets ought to be presumed to depend on their relation to the sun, 

 until the contrary appears ; and all the periodic motions of the satellites 

 ought to be presumed to depend upon their several planets. 



