304' Mr. Earnshaw on the Theory of the Dispersiofi of Light. 



nieme de doter la science d'une pile construite d'apres Ics 

 j)rincipes precedentes, et qui est aujourd'hui generalenient 

 adoptee dans les experiences de physique." 



It is only necessary to recall the data of my first paper upon 

 the subject in the Philosophical Transactions, viz. February 

 11th, 1836, and that of Prof. Grove's communication to the 

 French xVcademy, I believe, April 1839. Prof. Grove has 

 never spoken of his battery but as the further application of 

 principles which I had previously deduced. 



In conclusion, I cannot but express my regret that the filial 

 piety of M. Edmond Becquerel should have betrayed him into 

 an act of injustice by preferring a claim for his father which 

 is totally unsupported by the facts of the case, and from which 

 his well-earned reputation can derive no permanent extension. 

 I remain, dear Sir, 



Very faithfully yours, 

 King's College, London, J. F. Daniell. 



March 1842. 



To Richard Phillips, Esq., 8)X. Sfc. 



XLV. On the Theory of the Dispersion of Light. By S. Earn- 

 shaw, M.A., Cambridge. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



T HAVE observed with great interest the efforts which ma- 

 *- thematicians have made to establish the undulatory theory 

 of light on a firm basis. That theory (its fundamental hypo- 

 thesis being admitted) has succeeded so well in accounting for 

 a great variety of intricate and delicate phaenomena, that I am 

 not much surprised to observe that some of its leading ad- 

 mii-ers have adopted the opinion that its truth is now beyond 

 controversy. Among its greatest advocates, however, are some 

 who do not hesitate to allow that certain optical phtenomena 

 have not been fully accounted for on their favourite theory, 

 and that others have been as yet explained only in a doubtful 

 manner. I hope therefore that, without incurring the risk of 

 being reckoned an anti-undulationist, I n)ay be pei'mitted to 

 make a few remarks on that "opprobrium of all theories — the 

 dispersion of light." A compendious view of the present state 

 of this portion of the general theory of undulations may be 

 found in a book lately published by Professor Powell*. In 

 that work are contained several sets of tables, which exhibit, 



* The Undulatory Theory as applied to the Dispersion of Light, &c. 



