330 M. Edmond Becquerel on the Constant 



tion of constant voltaic batteries (appareils a courant constant), 

 and, as they still perfectly fulfil the purpose he had intended, 

 it is impossible to contend with him for the idea, the principle, 

 or the application within certain limits. 



The details into which I shall enter will leave no doubt 

 about the priority of invention, at least I hope so. For more 

 than fifteen years the electro-chemical reactions, by means of 

 which my father was enabled to obtain crystallized mineral 

 substances, were produced by the aid of small apparatus com- 

 posed of tubes in the form of the letter U, closed at their cur- 

 vature by a partition of moist clay designed to separate the 

 two liquids placed in the two branches of each tube, one of 

 which contained a solution of sulphate, nitrate or chloride of 

 copper in contact with a plate of copper, and the other con- 

 tained a solution of sea-salt, into which a plate of zinc or of 

 another metal was immersed. Such is the arrangement of 

 the simple apparatus which is scientifically known by the 

 name of pile a cloison*. 



The form of this apparatus is of little importance, since it 

 may be infinitely varied : for example, instead of a tube in 

 the form of a U, we may take any kind of vessel, separated 

 into two compartments by a diaphragm of bladder, baked 

 earth, plaster, or linen, &c. But all these various modifica- 

 tions enter into the principle of the U-tube. 



After the year 1829, and before Mr. DanielPs publication, 

 my father made several communications relating to the same 

 subject ; in fact, we find in the Compte Rendu des Seances de 

 VAcademie des Sciences for 1835, the description of an appa- 

 ratus giving a current which was sensibly constant for two 

 entire days. 



According to this, therefore, Mr. Daniell cannot pretend 

 to the discovery of the general principle on which the con- 

 struction of constant voltaic batteries rests, but he may justly 

 claim the good arrangement which he has given to his pile, 

 and, amongst others, the advantage of always having a satu- 

 rated solution of sulphate of copper, and of obtaining in a 

 small compass effects far more energetic than those for which 

 my father had occasion in the beginning, for the production 

 of crystallized substances analogous to those formed by na- 

 ture, a discovery for which he received the Copley Medal from 

 the Royal Society of London, and which Mr. Daniell himself 

 received some time after for the constant voltaic battery. 



Mr. Daniell, notwithstanding facts so evident, declares in his 



* An English translation of the description of this apparatus, and of 

 M. Becquerel's Researches on Crystallization produced by Voltaic Action, 

 was published in Taylor's Scientific Memoirs, Part 3. Jan. 1837. — Ed. 



