Dr. Draper on Mr. Hunt's Researches on Light. 49 



Oil of parietin . C40 Hjg 



Parietic acid . . C40 Hig Ojg 



Parietin . . . C40H16O14 



Oxide of parietin C^q Hig 0,g 

 I have found parietin in the Squamaria elegans {brought 

 from Cockburn Island, in 64° S. lat., by Dr. Joseph Hooker, 

 and styled by him " the most antarctic plant "), a fact which 

 adds strength to the idea of Mr. Griffith, that many of the co- 

 loured lichens, such as Lecatiora vitellina and concolor, Squa- 

 maria murorum, elegans, &c., are probably the Parmelia parie- 

 tina under different circumstances, as all these plants seem to 

 owe their colour to the presence of parietin. 



VI. On Mr. Hunfs Book, entitled "Researches on Light." 

 By Professor Draper. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 A COPY of Mr. Hunt's book, entitled " Researches on 

 ■^^^ Light," has been sent to me from London, and I sin- 

 cerely regret that I am called upon to express myself in dis- 

 approval both of its contents, and of the spirit in which it is 

 written. 



I must enter my protest against this book being received as 

 any authority in the science on which it professes to treat; 

 either as a work of history, or as an exposition of known facts. 



In a treatise which commences with the history of light 

 from the writings of Moses, and which professes to be " the 

 first history of photography which has been published," giving 

 "to every one his full share in those discoveries which have 

 accelerated the advancement of the art," there is not one word 

 in allusion to the application of the Daguerreotype to the taking 

 of portraits from the life; unquestionably the most important 

 application of the art isohich has yet been made, and which Mr. 

 Hunt k7iows belongs to me. 



There is scarcely an experiment of mine, to which allusion 

 is made, which is not either misrepresented or misunderstood. 

 Of the experiments of others I have nothing here to say. 



Against the spirit in which this volume is written I must 

 also protest. Any person who reads it through, without a 

 previous acquaintance with these matters, would rise from the 

 perusal of it with an impression that the science of photogra- 

 phy is the intellectual creation of Mr. Hunt, — that some very 

 good contributions to it have been made by Sir John Herschel, 

 and a few remarks here and there added by distant or obscure 

 experimenters. 



Now, Sir, this is all wrong. It is time that scientific men 



Phil. Mag. S. 3. Vol. 25. No. 163. July 1844. E 



