1898.] Mr Gadow, Orthogenetic Variation, etc. 35 



Everything is symmetrical about the axis of a ray, so that 

 each ray is a solid of revolution about the axis. In the case of 

 phenol the rays resemble paraboloids of revolution and are less 

 finely pointed when the supercooling is large than when it is 

 small. 



If <f> is the angle which a tangent plane to the surface of a 

 ray at a point P makes with the axis of the ray, then 



v sin <f> = G (0 O - 6), 



where v is the velocity of the point of the ray and 6 the tempe- 

 rature at P. 



At the tip of the ray v = C(0 o — 6 P ), where 9 P is the temperature 

 of the tip. 



When the supercooling is not too small so that v is considerable 

 dp — #! will be nearly zero, but when v is very small then 6 P — 6 t 

 may be considerable compared with 6 — 6 1 . Consequently when 

 the supercooling is very small the velocity will be smaller than 

 would be expected if the tip were supposed to be at the original 

 temperature of the liquid. This explains the small rate at which 

 the velocity increases with the supercooling when the supercooling 

 is very small. 



Monday, November 14, 1898. 

 Mr J. Larmor, President, in the Chair. 

 Mr A. Willey and Mr E. J. Bles were proposed for election. 



The following Communications were made to the Society: — 



(1) Orthogenetic variation in the shells of Chelonia. By 

 H. Gadow, F.R.S. 



The investigation is based upon 20 newly-hatched specimens 

 of the " Loggerhead " Turtle, Thalassochelys caretta, collected from 

 one nest by Dr Willey. This material was further supplemented 

 by 21 newly-hatched and 15 other specimens of all sizes. 



The variations are very numerous and manifold. The number 

 of median scutes varies from 8 to 7 to 6, and the lateral or costal 

 scutes range from 7 to 6 to 5, and they are either symmetrical or 

 uneven, there being perhaps 7 on the left and 6 on the right side, 

 or vice versa. 



These variations can be reduced to a system. 



3—2 



