Prof. Dove's Experiments in Magneto-Electricity. 33 



where C is a quantity whose total differential with respect to 

 t is zero. 



a. If C be an absolute constant, the equations for deter- 

 mining u and v are 



u 



d-u dK 

 dx* + dy*~ ' 



+ 



= 0. 



dx* ' dy* 

 b. If C be not an absolute constant, the equation for u as- 



sumes the following complicated shape : — 



ds 



ds du 



du ds 

 dx dy 



du 



dy 



du 

 dx' 



The equation for v is exactly similar to this. 



It is unnecessary to add that this equation is too complicated 

 to admit of integration in a general form. 



We shall not prosecute these remarks further ; we have 

 offered them rather for the purpose of directing attention to 

 the process than from a conviction of their novelty or im- 

 portance. 



VI. Experiments in Magneto-Electricity, illustrative of a 

 Passage in Professor Faraday's Researches. By Professor 

 Dove*. 



TJW.RADAY says, § 1101, " As an electric current acts by 

 induction with equal energy at the moment of its com- 

 mencement as at the moment of its cessation, but in a con- 

 trary direction, the reference of the effects of a current when 

 stopped to an inductive action would lead to the conclusion, 

 that corresponding effects of an opposite nature must occur 

 in a long wire, a helix or electro-magnet, every time that con- 

 tact is made with the electro-motor. These effects will tend 

 to establish a resistance for the first moment in the long con- 

 ductor, producing a result equivalent to the reverse of a shock 

 or spark. Now it is very difficult to devise means fit for the 

 recognition of .such negative results." This difficulty may, 



* Communicated by H. Croft, Esq., Teacher of Chemistry, being an ex- 

 tract from a letter addressed to him by the Author. 



Phil. Mag. S. 3. Vol. 2 1 . No. 1 35. July 1 84-2. D 



