the magnetizing power, and R the magnetic resistance, he assumes the 



relation analogous to Ohm's law : Z == (2), where R ^ K — . 



~ ' R S 



Here L is the length and 6" the section of the magnetic circuit, R being 

 the specific resistance. In dealing with iron Kapp finds that if the expres- 



r TT ^ 



tan I - f^) I 

 sion for R be multiplied bj a factor !^ 1 where n is the degree of 



saturation of the iron ; the resulting expression seems to represent the 



true magnetic resistance. This corrected value of Z, when substituted in 



ZnN' 



the equation for E, E = -z ^ (-i). 



' 60X108^-*^ 



Where N is the number of windings on the armature, gives an equa- 

 tion which is to hold in place of (i). 



The tangent function with which R is multiplied approaches unity as 

 P approaches zero, and it is well known that this result agrees well with 

 determined values. There is at present some uncertainty about the max- 

 imum number of lines that can be carried per square inch of section by 

 different irons when C is infinite. 



Dr. Adams spoke of the value of the work of Froelich, Deprez, 

 Hopkinson, and Kapp, as representatives of German, French and 

 English advanced practice in dynamo machine construction, and 

 as involving the modern theory of the dynamo, stating that the 

 crowning achievement was the creation of the formulae of Kapp 

 with their determined constants. 



December 20///, 1886. 



President Nipher in the chair ; ten members present. 



Prof. Pritchett submitted a paper on experimental determina- 

 tion of the value of ;r, based upon a discussion of the probability 

 of intersection when a rod of given length is thrown at random 

 across a system of parallel lines. Referred to the Committee of 

 Publication. 



Prof. Nipher remarked concerning the statement of Mr. Fitz- 

 gerald, of Boston, that there was probably no relation between 

 the readings of rain-gauges and wind ; that his conclusion was 

 probably due to the fact that the rain-gauges and wind-vanes 

 observed were nearly three miles apart, and would not be borne 



