88 Prof. G. Kirchhoff on the Measuring 



Putting, for further abbreviation, 



;U(«)-A»), 



the first part of p becomes 



» i s(-i)»/ ( /(2i±iy^ ± ^i ± ^Y 



far* v A» \ V X / 



The second portion can be written 



afcJ>(S)*<K)*(S)- 



or 



where, in taking the sum in reference to I and m, all the num- 

 bers from -co to +co are to be put for these symbols. To 

 calculate the member of this sum which corresponds to deter- 

 mined values of I and on, let us make 



U 2+ b 2 / 4 P 



with the condition that (3 is positive ; the term then be- 

 comes 



^(-D'2(-l)»£^ "T, 



where, in the summation, all numbers from — oc to + oo are 

 to be put for n, or 



+ ^u(/vx-^)}. 



For the case that /3 = 0, and that consequently Z and m are 

 simultaneously = 0, this result does not hold good ; the term 

 corresponding to these values of I and m is 



abk y/ it 

 or 



2 



abk^ir^, , K 



j>(3> 



f% CO W 2 C 2 



