536 



Tliis result is of course a quite natural one from a pnrel_y non- 

 mathematical point of view. Tlie shielding power of the micro- 

 residnally conducting la^^er at AB (Fig. 2) is extremely great on 

 account of its high conductivity. Thus in a finite thickness it trans- 

 mits practically no magnetic field and as long as the magnetic field 

 is transmitted the thickness of the microresidually conducting layer 

 must be very small. 



It is of interest to point out that even though the thickness of 

 the microresidually conducting layer is very small the resistance of 

 a square centimeter of this layer is finite and in the limit indepen- 

 dent of Ö,. In fact this resistance is: 



The formula (14) can be made clear also in the following manner. 

 The microresidually conducting layer has two boundaries : one at 

 X = and one at r = x,-. The value of H at the first is //, and 

 at the second it is He- The drop in H in the thickness Xc is 

 H^ — He- Let us suppose that this diop takes place uniformly throug- 

 hout the thickness Xc- Then the drop in H per unit length is 



— ^ throughout. This quantity divided by /?, is by (7) the elec- 



trie intensity E which must be continuous at the passage through 

 .r, = Xc- To the right of x = Xc the conditions for H are determined 

 by the facts that H = He for x = Xc and H::^ H^ for ,ï = 00. Since 

 Xc is practically zero we commit no sensible error by replacing the 

 first of these conditions by H =: He for x = 0. For this case it is 

 clear that: 



H = Hc + (fl -//e) (^ 1/7) 



and 



1 /'dH\ 1 2 — 



( ^ = —- ^(- /?, + He). 



17 jy 



Since this is the same as — ^ ^ the equation (14) follows. Thus 



?-,Xe 



the assumption of uniform drop of H in the microresidually con- 

 ducting layer leads to a correct result. 



Since Xe is very small it appears legitimate to generalize this 

 conclusion and to assume generally that H drops off uniformly 

 thi'oughout the microresidually conducting layer even in the general 



