360 M. Becquerel on an Electro-magnetic Balance, 



spirals similar to those just mentioned, except that they con- 

 sisted of two sets of circumvolutions, have been employed. I 

 have employed them for the purpose of determining the tem- 

 peratures of the several layers of the flame of an alcohol lamp 

 by means of two platina wires of different diameters joined 

 at one end. The temperatures were found to be 1310°'98, 

 913°-24., 74.3°-56. 



The instances adduced in this memoir are decisive as to the 

 facility with which, by means of weight, we may compare the 

 intensities of currents produced by electricities of different 

 tensions. 



If we wish to measure the continuous action of a force, we 

 must first endeavour to give it an unvarying intensity. But 

 the electric current produced by the common piles, and even 

 by a single pair, is liable to continual variations, which render 

 it impossible to make its mode of action the subject of calcu- 

 lation. In order to obviate this inconvenience I have con- 

 structed a pile which produces a current whose intensity suf- 

 fers no sensible variation for twenty-four, and in some instances 

 for forty-eight hours. 



Some years since I made public a very simple apparatus 

 producing a current varying but little during a given time. It 

 consists of two small glass phials ; one containing concen- 

 trated nitric acid, and the other a solution of caustic potash, 

 also concentrated. The two phials communicate with each 

 other by means of a bent glass tube, filled with very fine clay 

 moistened with a solution of sea-salt. Into the phial contain- 

 ing the alkali I plunge a plate of gold, and into the other a 

 plate of platina. When the two plates are brought into com- 

 munication with a multiplier, a current of considerable energy 

 is found to result from the reaction of the acid on the sea-salt 

 and the potash. The plate of gold takes the negative elec- 

 tricity to the alkali, and the plate of platina carries the positive 

 electricity to the acid. 



In order to obtain the maximum effect, due attention must 

 be given, in the construction of this apparatus, to the fol- 

 lowing considerations. Were it possible to transform into a 

 current all the electricity that is disengaged in the combina- 

 tion of a given quantity of acid with a proportionate quantity 

 of alkali, this current would, in its turn, decompose all the 

 salt that is formed. Accordingly, if in the reaction of an acid 

 on an alkali we can direct a sufficient portion of the electri- 

 cities disengaged, we shall have a current of sufficient inten- 

 sity to produce decompositions. For the purpose of partially 

 attaining this condition, we take two tubes of platina, each 

 being bent at one end, in order that it may be inserted into 

 a glass tube. One of the platina tubes is filled with clay 



