56 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXVIII.) 
it be understood, that, wherever the expression line offeree is taken simply to repre- 
sent the disposition of the forces, it shall have the fullness of that meaning ; but that 
wherever it may seem to represent the idea of the physical mode of transmission of 
the force, it expresses in that respect the opinion to which 1 incline at present. The 
opinion may be erroneous, and yet all that relates or refers to the disposition of the 
force will remain the same. 
3176. The value of the moving wire or conductor, as an examiner of the magnetic 
forces, appears to me very great, because it touches the physics of the subject in a 
manner altogether different to the magnetic needle. It not only gives its indications 
upon a different principle and in a different manner, but in the mutual action of it 
and the source of power, it affects the power differently. The wire when quiescent 
does not sensibly disturb the arrangement of the force in the magnetic field ; the 
needle when present does. When the wire is moving it does not sensibly disturb the 
forces external to it, unless perhaps in large masses, as in the discs (3163.), or when 
time is concerned (1730.), i.e. it does not disturb the disposition of the whole force, 
or the arrangement of the lines of force ; a field of equal magnetic power is still equal 
to anything but the moving wire, whilst the wire moves across or through it. The 
moving wire also indicates quantity of force, independent of tension (2870.) ; it 
shows that the quantity within a magnet and that outside is the same, though the 
tension be very different. In addition to these advantageous points, the principle is 
available within magnets, and paramagnetic and diamagnetic bodies, so as to have 
an application beyond that of the needle, and thus give experimental evidence, of a 
nature not otherwise attainable. 
Royal Institution, 
October 9, 1851. 
