Royal Society. 211 



Now, if the picture which has been tlius washed and di-ied 

 is placed in the sun, the white parts colour themselves of a 

 pale lilac tint, after which they become insensible. Numerous 

 experiments have shown to me that the depth of this lilac tint 

 varies according to the quantity of salt used, relatively to the 

 quantity of silver. But, by properly adjusting these, the 

 images may, if desired, be retained of an absolute whiteness. 

 I find I have omitted to mention that those preserved by iodine 

 are always of a very pale primrose yellow; which has the ex- 

 traordinary and very remarkable property of turning to a full 

 gaudy yellow whenever it is exposed to the heat of a fire, and 

 recovering its former colour again when it is cold. 



I am, &c. 



H. Fox Talbot. 



XXXVIII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 

 [Continued from p. 141.] 

 Dec. 6, 1838. — A paper was in part read, entitled, " Experi- 

 mental Researches in Electricity." Fifteenth Series. — " Note of the 

 Character and Direction of the Electric Force of the Gymnotus." 

 By Michael Faraday, Esq., D.C.L., F.R.S., &c. 



Dec. 13, 1838 — The reading of a paper, entitled, "Experimental 

 Researches in Electricity." Fifteenth Series* — "Note of the Cha- 

 racter and Direction of the Electric Force of the Gymnotus." By 

 Michael Faraday, Esq., D.C.L., F.R.S., &c., was resumed and con- 

 cluded. 



The author first briefly refers to what has been done by others in 

 establishing the identity of the peculiar power in the Gymnotus and 

 Toqiedo with ordinary electricity, and then in reference to the in- 

 tended conveyance to this country of Gymnoti from abroad, gives 

 the instructions which he himself had received from Baron Humboldt 

 for that purpose. A living Gymnotus, now in the possession of the 

 Proprietors of the Gallerj' of Science in Adelaide Street, was placed 

 for a time at the disposal of the author for the purpose of research, 

 upon which he proceeded, with suitable apparatus, to compare its 

 power with ordinary and voltaic electricity, and to obtain the direction 

 of the force. Without removing it from the water he Avas able to ob- 

 tain not only the results procured by others, but the other electrical 

 phenomena required so as to leave no gap or deficiency in the evi- 

 dence of identity. The shock, in very varied circumstances of posi- 

 tion, was procured: the galvanometer affected ; magnets were made; 

 a wire was heated ; polar chemical decomposition was effected, and 

 the spark obtained. By comparative experiments made with the 



* Prof. Fi.raday'.s prc-ccding scries of Exj). Res. in Electricity have been 

 given, cither entire or in abstract, in various volumes of Lond. and Edinb. 

 Phil. Mag.— Eurr. 



P2 



