XXII 



duction of the spectrum in its natural colours, with the serious 

 drawback that the coloured image could be preserved only in com- 

 plete darkness. Our advances upon Becquerel in this direction have 

 not been so rapid or decisive as might have been hoped. 



Becquerel came to the conclusion that all the effects produced 

 under the influence of light are due to one. and the same radiation 

 acting upon different bodies. He considered it probable that in 

 different beings the retina is not always sensitive between the same 

 limits of refrangibility. His principal researches in this direction are 

 to be found in the ' Annales de Chimie ' for November, 1848. 



It must not be forgotten that Becquerel's view was strongly 

 opposed by Professor Forbes, of King's College, also by R. Crouch, of 

 Polperro, who both maintained that no marine animal has the power 

 of vision under the influence of such rays of light as would not excite 

 the optic nerve of man, and that those depths of the ocean at which 

 an everlasting darkness prevails, are the regions of silence and death. 



It need scarcely be said that recent research has fully proved that 

 existing animal species can recognise rays of light which make no 

 impression on the human retina, thus confirming the correctness of 

 Becquerel and refuting his critics. 



It is not surprising that with the researches just mentioned he 

 combined a prolonged and exhaustive study of phosphorescence as 

 produced by insolation. 



For the better study of these phenomena, he invented his well- 

 known phosphoroscope. By means of this instrument, substances 

 can be viewed immediately after having been exposed to the light of 

 the sun ; the interval between insolation and observation being 

 capable of reduction at pleasure and of very accurate measurement. 

 Edmond Becquerel investigated also the light emitted by the phosphor- 

 escent compounds of uranium, and turned his attention to the infra- 

 red portion of the spectrum, and to the ultra-violet portion, to which 

 the chemical action involved in the new art of photography was due. 

 He formed a pure spectrum on a sensitive plate of silver prepared by 

 the process of Daguerre, and found that the fixed dark lines of the 

 solar spectrum as recognised by Wollaston, Fraunhofer, and 

 Brewster were traceable in the chemical impression, and that similar 

 lines therefore existed in the parts of the solar spectrum lying beyond 

 the limits of visibility. Becquerel published in the ' Bibliotheque 

 Universelle de Geneve ' for 1842 a diagram of the fixed lines of the 

 spectrum as enlarged by these researches. These photo-chemical and 

 optical studies, taken conjointly, have been pronounced by Fizeau to 

 be a model of research in experimental physics. 



Another research of the highest order was his investigation of the 

 action of magnetism on all substances, especially upon oxygen, the 

 magnetic function oi which he carefully scrutinised. Here he and 



