igi liayal Society. 



theory, so far as it went (which in the way of explanation was 

 not a great way), I was led to the above conchisions while in 

 search of a more intelligible mode of accounting for the phae- 

 nomena than Fresnel's appeared to be, and which I naturally 

 sought in the only direction in which, assuming the trust- 

 worthiness of his experiments, it could be found, namely by 

 consideration of the effect of the diffraction of the waves them- 

 selves abstracted from any specific action of the diffracting 

 body. But I must confess that since that time my faith in 

 Fresnel's merits as an experimentalist, as well as a theorist, 

 have been greatly shaken, and that I do not feel the degree 

 of confidence which I once entertained as to the truth of the 

 position which he assumes himself to have established by ex- 

 periment, " that diffraction is independent of the nature of the 

 diffracting body and of the form of its edge." But if this be 

 not the case. Dr. Young's theory of diffraction is at once 

 revived ; and thus this point of fact forms an experimentum 

 cruets as to whether his theory or mine is to be received. If 

 Fresnel's conclusion be contrary to the fact, and the diffrac- 

 tion is dependent on the nature of the diffracting body, my 

 theory cannot well be true and his cannot well be false, and 

 vice versa. But whatever be the conclusion we may ultimately 

 come to upon this point, and to experimentalists I leave it, 

 the above suggestions may not be without their use; first, as 

 directing attention to the nature of the motion of discontinu- 

 ous waves, a subject which has never hitherto been discussed 

 in any intelligible manner; and secondly, as thereby affording 

 a clearer and more certain elucidation than has ever yet been 

 given of that remarkable phaenomenon usually referred to, by 

 saying that "light will not penetrate round a corner." 



I hope to have an opportunity at an early period of enter- 

 ing upon the consideration of Fresnel's theory of polarized 

 light and of double refraction. 



10 Maddox Street, Bond Street, 

 June 13, 1845. 



XIV. Proceedings of Learned Societies. 



ROYAL SOCIETY. 

 [Continued frcna vol. xxvi. p. 539.] 

 May 22, " IV/f EMOIR on the Rotation of Crops, and on the 

 1845. ^^ Quantity of Inorganic Matters abstracted from 

 the Soil by various plants under different circunistances." By 

 Charles Daubeny, M.D., F.ll.S., Professor of Rural Economy, &c. 

 in the University of Oxford. 



The author was first led to undertake the researches of wliich an 

 account is given in the present memoir, by the expectation of verify- 



