Forces of some Metallic Alloys in Contact with Copper, 29 



took, in the beginning of the year 1872, a similar investigation 

 of various alloys. The present memoir contains the results, the 

 investigation having been carried out in the physical laboratory 

 of the Royal Swedish Academy of Sciences, Stockholm. 



1. M. Edlund's method is based on the proposition, de- 

 duced from the mechanical theory of heat, that a galvanic cur- 

 rent going through an electromotor calls forth in it an absorp- 

 tion or production of heat proportional to its electromotive force, 

 according as the current is in direction the same as or opposite 

 to that generated by the electromotor itself*. Hence the rela- 

 tive quantity of the electromotive force is obtained by measuring 

 the amount of heat absorbed or produced. The phenomenon 

 also indicates, as is readily seen, the direction of the current ex- 

 cited by the electromotor. 



The air-thermometer constructed by Professor Edlund for the 

 measurement of the quantities of heat in question is fully de- 

 scribed in his memoir ; consequently it will be sufficient here to 

 mention only the principal parts of this apparatus. Two per- 

 fectly equal cylinders of thin sheet copper communicate through 

 a horizontal glass tube of 2*5 millims. internal diameter. Into 

 both cylinders, through open tubes which enter the middle points 

 of their ends, the same combination of two metals in the shape 

 of wires or rods is inserted in such wise that the place of contact 

 is in the centre of the cylinder. The tubes are lined internally, 

 to half their length, with wood, to prevent contact between the 

 cylinder and the wire. Communication between the outer air 

 and that of the cylinder is then completely cut off by pouring 

 into the tubes a melted mixture of equal parts by weight of wax 

 and rosin. The two wires are inserted in the circuit of a gal- 

 vanic current in such a manner that, when the current in one 

 of the wires goes from metal A to metal B, the second wire is 

 passed through by the current in the opposite direction, from 

 B to A. Hence arises at the one place of contact a production, 

 at the other an absorption, of heat. The trifling difference 

 hereby produced between the temperatures of the air in the cy- 

 linders occasions the displacement of a column a few centimetres 

 long of liquid in the tube, a mixture of alcohol and water of sp. 

 gr. 0*9 which acts as an index. If the current be reversed, a 

 cooling ensues in the cylinder in which there was previously a 

 heating, and vice versa, by which the index is moved towards the 

 opposite side. The displacement towards the one side or the 

 other ceases as soon as equilibrium is restored between the heat 

 given off by each cylinder through radiation and conduction to 



* This proposition was first advanced by Professor Edlund ( (Efv. af K. 

 Vet.-Akad. Forh. 1869, p. 457; Pogg. Ann. vol. cxxxvh. p. 4/4 \ Phil.! 

 S. 4. vol. xxxviii. p. 2(i3). 



