Geological Society. 639 



dy 

 Take as a type the simple case of the D.E. -=- = j^x. 



The solution of the D.E. of the second order with constant 



coefficients is implied tacitly in all treatises on Physics, in the 



d 2 x 

 form -r^-f- n 2 #=i0 for simple vibration, and the penultimate 



pendulum oscillation. 



We put in a plea here for a return to Aristotle's name of 

 Centre of Gravity, instead of the variants coming in of centroid, 

 centre of mass, of figure, of volume, of inertia. 



A mental reservation is implied here of the effect of a radiating 

 field of gravity, on a body according as it is non-centrobaric. This 

 is a refinement that cannot be detected in a careful weighing in a 

 balance, the most accurate operation in a measurement in Physics. 



Call the areal coordinates of § 460 centrobaric, and extend the 

 idea to any number of particles, to make great use of the idea in 

 a number of dynamical problems. 



Colonel Hippisley's Ephelkustikon curves deserve mention, as 

 described by a jointed tail, leading sometimes to a good illus- 

 tration of the asymptotic circle, encountered in some central 

 orbits. 



The figures are careful and accurate ; and we are spared the 

 too frequent footnote. 



There is a copious Table of Contents, but no Index. 



LXXV. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from vol. xlii. p. 1024.] 



December 7th, 1921.— Mr. H. G. Oldham, F.E.S., President, 

 in the Chair. 



^T^HE following communications were read : — 



1. ' Jurassic Chronology : II. — Preliminary Studies. Certain 

 Jurassic Strata near Eype's Mouth (Dorset) : the Junction-Bed of 

 Watton Cliff and Associated Rocks.' By S. S. Buckman, F.Gr.S. 



This paper deals Avith certain Jurassic strata near Eype's Month 

 on the coast of Dorset ; but, as it forms part of a series of pre- 

 liminary studies in connexion with Jurassic chronology, certain 

 details connected with other localities are noticed. A general 

 section of the main mass of Watton Cliff east of Eype's Mouth is 

 given. A detailed section is recorded of a remarkable white litho- 

 graphic bed in Watton Cliff, one in the same position as the 

 Junction-Bed, but differing much in faunal and in stratal details. 

 This bed shows faunal inversion, presumably due to redeposition of 

 material from older deposits. 



