330 HERMANN VON HELMHOLTZ 



dielectric upon a surface-element, the normal to which forms a 

 given angle with the direction of the lines of force, and a tension 

 that is effective in the direction of the same. Helmholtz finally 

 concludes from the expressions for the forces, that the two 

 views that, namely, which postulates forces acting at a distance, 

 and that of Faraday- Maxwell, according to which there is only 

 polarization of the media may thus exist side by side. 



At the same time Helmholtz published a brief notice in 

 Wiedemanris Annalen on 'An Electrodynamic Balance', which 

 he had constructed with the object of avoiding, in the measure- 

 ment of galvanic currents in absolute measure, the disturbances 

 which the changes in the direction and intensity of the earth's 

 magnetism produce by their electromagnetic action. At the 

 ends of the beam of a small chemical balance, he suspended two 

 coils of copper wire, the height of which is equal to their in- 

 ternal diameter, the axes being vertical ; two coils of the same 

 height and greater radius were held in a fixed position some- 

 what above the movable coils by a horizontal metal bar, fixed 

 by its centre to the pillar that carries the balance. The con- 

 nexions of the wires are so arranged that one of the movable 

 coils is attracted and the other repelled by the fixed coils ; the 

 attracted coil rises, the repelled sinks, when current is passed 

 through the circuit, each of the movable coils being connected 

 with the wires that carry the current by two strips of brass foil. 

 The total action of both coils is maintained in equilibrium by 

 appropriate weights, so that the force which opposes the electro- 

 dynamic force, and measures it, is subject to gravity alone, with 

 no variations, such as affect the earth's magnetism. 



In the Easter holidays of 1881 Helmholtz went to London 

 with his wife at the invitation of the Chemical Society to give a 

 Lecture in the place * in which the great investigator Faraday, 

 whose memory was to be honoured, had so often surprised his 

 admiring audience by his revelations of the unsuspected secrets 

 of nature '. 



His discourse on 'The Recent Development of Faraday's 

 Ideas on Electricity ' (delivered in English, after Roscoe had 

 read it through and altered a few expressions) ranks from its 

 form and content among the most beautiful and profound of his 

 Addresses. 



'His Faraday Lecture/ writes his wife, 'was a brilliant success. 



