502 Prof. Maskelyne and Dr. Lang's Mineralogical Notes. 



The applications of my hydrodynamical researches which I 

 have made from time to time in the nndulatory theory of light, 

 have now embraced most of the leading phenomena, excepting 

 that hitherto I have not indicated their application to the phe- 

 nomena of Diffraction. The theoretical explanations that have 

 been given of this class of facts rest mainly on an assumed law 

 of limited lateral divergence, and on this assumption have been 

 successful. Now, from reasoning contained in this and previous 

 communications, I am justified in inferring that this law is a 

 consequence of the composite character of waves, and of the 

 circumstance that the component vibrations are partly direct 

 and partly transversal. Also the supposition usually made in 

 the mathematical treatment of problems of diffraction, that the 

 waves are compounded of indefinitely small parts each possessing 

 the property of limited lateral divergence, is in accordance with 

 this hydrodynamical theory of the composition of waves. I 

 have never been able to perceive how such a supposition is con- 

 sistent with a theory of light which regards the aether as com- 

 posed of discrete atoms. On the whole the results of my re- 

 searches give reasons for the conclusion that the undulatory 

 theory of light rests legitimately on no other than a hydro- 

 dynamical basis. 



Cambridge, November 21, 1864. 



LXII. Mineralogical Notes. By Professor N. S. Maskelyne 



and Dr. Viktor von Lang, of the British Museum. 



[Continued from p. 150.] 



[With a' Plate.] 



On the Crystalline Form of Malachite. By Viktor von Lang. 



AFTER I had published my first Note on this subject I came, 

 in the mineral collection of the British Museum, upon 

 several more tolerably well crystallized specimens of malachite, of 

 which the following is a description. These new observations 

 not only confirmed my previous ones, but also led me, as I 

 believe, to a somewhat more accurate determination of the cry- 

 stallographic elements of malachite, viz. 



a : b : c = 07823 : 1 : 0*4036. 



ac = 90° 3'. 



They were deduced from the angles 



110.110=75 56 

 101.100 = 61 53 

 103.100 = 98 43, 



