THE DIVIDING CELL 



337 



on either side will converge inward — be " refracted " to crowd 

 into the body ; and if its permeability be infinite, they will enter 

 it normal to the surface (fig. 5). 



If we shake up fine magnetic dust over a rough surface, 

 we have a dust-cloud, in which the particles can turn lengthwise 

 to the lines of force ; and if the cloud were permanent they 

 would float along the lines to the nearer pole ; but falling 

 immediately as they do, they are retained by the friction of the 

 surface in the position which they had momentarily assumed. 



If now we suspend the magnetic dust in a viscid liquid, 

 the particles arrange themselves loosely into filaments extending 

 from pole to pole as a spindle with circumpolar radiations ; but 



Fig. 5. — Magnetic dust-chains on paper showing (a) refraction into and out of an interposed 

 inductor or more permeable body — an iron ring ; {b) screening action of a hollow 

 inductor on the space within. 



these filaments remain stretching across because of the viscidity 

 of the medium, corresponding to the friction of the surface in 

 the previous case. I have called this configuration of matter of 

 filaments of more permeable material segregated from admixture 

 with a less permeable fluid medium under the stresses of a 

 centred force, "material chains of force," or, simply, "chains 

 of force." Such chains in a viscid medium may be regarded as 

 flexible bodies of higher permeability than the medium (or 

 briefly as " inductors "), and have characteristics of their own. 



(1) Owing to their greater permeability they contain more 

 unit lines of force per unit of cross-section than the surrounding 

 medium. 



