28 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXVIII.) 
cations as compared to those of a magnetic needle, and to show how it becomes a 
peculiar and important addition to it, in the illustration of magnetic action. 
30/8. The moving wire produces its greatest effect and indication, not when pass- 
ing from stronger to weaker places, or the reverse, but when moving in places of 
equal action, i. e. transversely across the lines offeree (2l7.). 
3079. It determines the direction of the polarity by an effect entirely independent 
of pointing or such like results of attraction or repulsion ; i. e. by the direction of the 
electric current produced in it during the motion*. 
3080. The principle can be applied to the examination of the forces within nume- 
rous solid bodies, as the metals, as well as outside in the air. It is not often embar- 
rassed by the difference of the surrounding media, and can be used in fluids, gases or 
a vacuum with equal facility. Hence it can penetrate and be employed where the 
needle is forbidden ; and in other cases where the needle might be resorted to, though 
greatly embarrassed by the media around it, the moving wire may be used with an 
immediate result (3142.). 
3081. The method can even be applied with equal facility to the interior of a mag- 
net (3116.), a place utterly inaccessible to the magnetic needle. 
3082. The moving wire can be made to sum up or give the resultant at once of the 
magnetic action at many different places, i. e. the action due to an area or section of 
the lines of force, and so supply experimental comparisons which the needle could 
not give, except with very great labour, and then imperfectly. Whether the wire 
moves directly or obliquely across the lines of force, in one direction or another, it 
sums up, with the same accuracy in principle, the amount of the forces represented 
by the lines it has crossed (31 13.). 
3083. So a moving wire may be accepted as a correct philosophical indication of 
the presence of magnetic force. Illustrations of the capabilities already referred to, 
will arise and be pointed out in the present paper ; and though its sensibility does not 
as yet approach to that of the magnetic needle, still, there is no doubt that it may 
be very greatly increased. The diversity of its possible arrangements, and the great 
advantage of that diversity, is already very manifest to myself. Though both it and 
the needle depend for their results upon essential characters and qualities of the 
magnetic force, yet those which are influential, and, therefore indicated, in the one 
case, are very different from those which are active in the other ; I mean, as far as we 
have been able as yet to refer directly the effects to essential characters : and this 
difference may, hereafter, enable the wire to a give a new insight into the nature of 
the magnetic force; and so it may, finally, bear upon inquiries, such as whether 
magnetic polarity is axial or dependent upon transverse lateral conditions ; whether 
* A natural standard of this polarity may be obtained, by referring to the lines of force of the earth, in the 
northern hemisphere, thus : — if a person with arms extended move forward in these latitudes, then the direc- 
tion of the electric current, which would tend to be produced in a wire represented by the arms, would be from 
the right-hand through the arm and body towards the left. 
