Cambridge Philosophical Society. 71 



full-grown Per. nasuta. I notice it to mention that the teeth 

 are, in all respects, similar to those of Per. nasuta, both in form and 

 number. 



The collection contains besides, two very fine specimens of Pe- 

 taurus Taguanoides ; one of Pet. Sciureus; one of Hydromys chryso- 

 gaster ; and a young Koala." — W. O. 



PROCEEDINGS AT THE FRIDAY EVENING MEETINGS OF THE 

 MEMBERS OF THE liOYAL INSTITUTION. 



March 25. — Mr. Goadby on Insect Anatomy. 



April 15, — Sir James South on Astronomical Observations as car- 

 ried on in the fixed Observatory. 



April 22. — Sir James South. The same (concluded). 



April 29. — Mr. Faraday on Plumbago and Pencils. 



May 6. — Mr, Daniell on a new and constant Voltaic Battery. 



May 13. — Dr. Lardner on Steam communication with India (con- 

 cluded). 



May 20. — Professor Mavo on some of the uses of Sensation. 



May 27. — Mr. Pettigrew unrolled an Egyptian Mummy. 



June 3. — Mr. Beamish on the pi'esent state and prospects of the 

 Thames Tunnel. 



Jnne 10. — Mr. Faraday. Considerations respecting the nature of 

 Chemical Elements. 



CAMBRIDGE rHILOSOPHICAL SOCIETY. 



[Continued from vol. viii. p. 431.] i 



A meeting of the Philosophical Society was held on Monday 

 evening, April 18th, Dr. Clark, the President, in the chair. The 

 Astronomer Royal (lately Prof. Airy) read a communication on the 

 intensity of light in the neighbourhood of a caustic. One object 

 of this investigation was to determine what must be the circum- 

 stances of the rainbow on the undulatory theory of light. After- 

 wards Mr. Hopkins gave an account of the agreement between the 

 results of his theory of elevatory geological forces, and the phae- 

 nomena of faults, as observed by him in the strata of Derbyshire. 



A meeting of this Society was held on Monday evening. May 2nd, 

 Dr. Thackeray, Vice-President, in the chair. A memoir was read 

 by S. Earnshaw, Esq., St. John's, " On the Integration of the Equa- 

 tion of Continuity of Fluids in Motion •" also a memoir by Professor 

 Miller on the Measurements of the Axes of Optical Elasticity of 

 certain Crystals. This memoir contained various determinations, 

 from which it appears that the law concerning the connexion of the 

 crystalline and the optical properties of crystals suggested by Pro- 

 fessor Neumann, namely, that the optical axes are the axes of cry- 

 stalline simplicity, is false; but that it is true, in many of the cases 

 hitherto examined, that one of the optical axes coincides with the 

 axis of a principal crystalline zone. Afterwards Mr. Webster, of Tri- 

 nity College, made some observations on the periodical and occa- 



