ELECTRICAL PROBING WITH AN APPARATUS IN WATER 



179 



where K is an instrumental coefficient (the apparatus placed at the water 

 surface) determined for the condition that in a homogeneous medium, 

 the value of q is equal to the true specific resistance of this me- 

 dium. 



If this condition is also taken as a basis of determining the coefficient for 

 instrument at the bottom, then the coefficient of the bottom apparatus 

 will depend not only on the geometrical dimensions of the latter but also 

 on the relative depth of its immiersion. 



It can readily be shown that in the general case of 4-electrode symmetry 

 of the apparatus, immersed to a depth h, the coefficient K^ can be expressed 

 in the following way: 



Km = K- 



t'+* 



(i)' 



+ 4 



Since Kj^j = MK, where 



M 



+ 4 



2(^1+4 



depends only on — , the shape of the curves obtained experimentally and 

 h 



theoretically changes in exactly the same way if, for these and others, 



the coefficient K is used instead of Kj^. 



Under working conditions it is more convenient to use the coefficient K 

 instead oiKj^, since the values of iiTfor various types of apparatus are calculat- 

 ed and given in nomograms. In calculating the theoretical curves for sea 

 probing with an apparatus at the bottom, the change in the coefficient of 

 the apparatus on being immersed to the bottom was therefore not taken 

 into consideration. 



We represent the apparent resistance, measured by the bottom apparatus, 

 as Qj^^ (without correcting the coefficient of the immersed apparatus). 

 The apparent specific resistance of the AMNB apparatus for MN->0 is 

 determined from the formula 



Q = 27ir^ 



E 



12* 



