Geological Society. 331 



really exist, and that the expression for the internal radiation is in- 

 dependent of the position of the surface. 



For the extraordinary ray, the internal radiation is found to be 



R - R? ' 4 



where R is the radiation from lamp-black ; 

 and for the ordinary, R =_ ; 



ZlTi 



where n denotes the axial and m the equatorial radius of the 

 ellipsoid into which the extraordinary ray will have spread in the 

 crystal in the same time that in vacuo it would have spread into a 

 sphere whose radius = unity ; and lastly, r denotes the radius of this 

 ellipsoid in the direction hi which the internal radiation is measured. 



The author concludes by remarking that .the fundamental law, 

 which is intimately connected with the theory of exchanges, and 

 which renders an equilibrium of temperature possible in the case 

 under consideration, seems to be the law of the equality between 

 action and reaction in the impact of elastic bodies. 



He also considers that the law which is expressed by saying 

 " That the absorption of a particle is equal to its radiation, and that 

 for every description of heat," expresses another law of action and 

 reaction which holds when the motion which constitutes radiant heat 

 is not conveyed from particle to particle without loss, or when the 

 bodies under consideration are not perfectly elastic. 



These two laws of action and reaction are viewed as supplement- 

 ing each other, so as to render that equilibrium of temperature which 

 is demanded by the theory of exchanges possible under all circum- 

 stances. 



GEOLOGICAL SOCIETY. 



[Continued from p. 244.] 

 January 22, 1862.— Sir R. I. Murchison, V.P.G.S., in the Chair. 

 The following communications were read : — 



1. "On some Flint Arrow-heads (?) from near Baggy Point, North 

 Devon." By N. Whitley, Esq. 



Immediately beneath the surface-soil above the " raised beaches " 

 of North Devon and Cornwall the author has observed broken flints ; 

 and even at the Scilly Isles such flints are found. At Croyde Bay, 

 about halfway between Middle-Borough and Baggy Point, at the 

 mouth of a small transverse valley, Mr. Whitley found them in con- 

 siderable number, collecting about 200 specimens, of which about 10 

 per cent, of the splintered flints at this place have more or less of an 

 arrow-head form, but they pass by insensible gradations from what 

 appear to be perfect arrow-heads of human manufacture to such rough 

 splinters as are evidently the result of natural causes. Hence the 

 author suggested that great caution should be used in judging what 

 flints have been naturally, and what have been artificially shaped. 



2. " On some further Discoveries of Flint Implements in the Gravel 

 near Bedford." By James Wyatt, Esq., F.G.S. 



Since Mr. Prestwich described the occurrence of flint implements, 



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