7 i Cambridge Philosophical Society, 



turc. He also stated that corrections had recently been discovered 

 to be necessary in the results of the Trigonometrical Survey of this 

 county, by which thp differences which had previously appeared to 

 exist between the astronomical andgeodetical determinations of the 

 latitude and longitude of Cambridge Observatory are greatly dimi- 

 nished. Mr. Stevenson, of Trinity College, read a memoir on the esta- 

 blishment of the formulae of Analytical Geometry by the combination 

 of the infinitesimal method with the doctrine of projections. Prof. 

 Sedgwick and other members then communicated some observations 

 illustrative of the geology of Cambridge. The upper chalk with flints 

 runs in a distinct terrace from near Newmarket, by Balsham and 

 Linton, to Royston Downs, and thence into Hertfordshire. Beneath 

 this is the lower chalk without flints, which runs from Reach to 

 Cherryhinton and Haslingfield. Below this is a thin bed, which re- 

 presents the upper greensand, and which, though not above a foot 

 and a half thick, is remarkably continuous in the neighbourhood of 

 Cambridge, being found at the Castle Hill, Barnwell, Ditton, Coton, 

 and Modingley. Under this are the blue gait and the " lower green- 

 sand" of geologists, which may here be called the red-sand. The 

 red-sand runs from Gamlingay and Caxton, by Conington, Long- 

 stanton, Cottenham, and Upware. But the junction of the gait and 

 red-sand is covered up on the west of Cambridge by a large diluvial 

 patch of " brown clay," which is full of rounded nodules of chalk. 

 This brown clay forms an upland, which extends from Bourne, by 

 Toft and Hardwicke, to Dry Drayton, after which it soon drops 

 into the plain; but the junction of the strata in the plain is still co- 

 vered up with ferruginous gravel as at Okington. Below the red- 

 sand occur other clays, easily confounded with the gait, but iden- 

 tified with the Kimmeridge and Oxford clays by their fossils ; these 

 are found at Graijsden, Cottenham Fen, and Ely. It was stated 

 that the relations of the successive formations are very obscurely 

 exhibited, in consequence of the strata and their junctions being 

 masked by diluvial masses. 



Dec. 8. — Prof. Airy, V.P., in the chair. Prof. Miller read a memoir 

 on the position of the Optical Axes of Crystals. Prof. Henslow 

 noticed some newly observed localities of the (upper) green-sand 

 in the neighbourhood of Barton and Haslingfield. He then made 

 some remarks on De Candolle's rules for determining the age of 

 trees, and mentioned some instances which he had noticed during 

 the preceding summer, in which they did not apply in the case of 

 the yew. He conceived that these rules, when applied to several 

 well known yew-trees in Britain, must give the age considerably too 

 great. Prof. Airy mentioned the echo which is returned by the open 

 end of the tall chimney recently erected at Barnwell gas-works. Prof. 

 Gumming then gave a statement of Melloni's discoveries on the 

 transmission of heat by radiation through glass and crystallized 

 bodies, illustrated by apparatus and experiments. 



