514 Dr. A. D. Waller. Various Inclinations of the [Mar. 6, 



line VP, drawn perpendicular to this zero line MO, gives the position of 

 the current-axis CC forming with the vertical MV an angle, which call «. 



The angle MOV = a ; tan a = tan MOV = MV/OV = \ = 0"5. There- 

 fore « = 26° 36' ; or otherwise : since MV = \ (L-E) and OV = \ (L + E), 

 we may write tan a = (L— E)/(L + E), or, in words, the required angle a 

 is an angle having for its tangent the fraction of which the numerator is the 

 difference between the spike of the strong lead and that of the weak lead, 

 and the denominator their sum. 



The formula holds good for negative values of the weak lead, as can easily 

 be shown by a geometrical construction. But an example will be sufficient. 

 Let —1 be the value observed by the weak lead E, and +3 that for the 

 strong lead L. 



tm * = mhBH- •••-= 64 °- 



Finally, we may mention two particular cases that are occasionally observed. 

 If the weak lead E = 0, then 



tan a = ^ — ^ = 1, .". a = 45°. 

 L + 



If the weak lead E is negative and greater than the strong lead we shall 

 have « greater than 90°, i.e. a current-axis upwards from right to left. This 

 case may also occasionally be met with as an extreme case of the " cor breve 

 et molle," e.g. let E = — 2 and L = 1, 



L — E 1 + 2 2 1 1 co 



tana= LTE = I32 = - 1 =- 2 ' - * = 116 - 



An essentially similar principle of calculation is applicable to the data 

 afforded by leads from the four extremities — the two hands and the two feet 

 — with, however, certain modifications. 



The modifications to be taken into account are : (1) that the two feet are 

 assumed to be equipotential and represented by a single foot F at the 

 inferior angle of the triangle ELF in analogy with the point M of our first 

 triangle ; (2) that therefore we are to regard as equivalent the right lateral 

 r V L O with the axial leads, and the left lateral with the 

 equatorial ; (3) that we have to remember that with 

 the extremities, E is the strong lead, L the weak lead ; 

 and (4) that the conditions require us to take at F a 

 more acute angle than in the case of the superior 

 triangle we have taken at M. 



In the figure representing the inferior triangle 

 the length VF has been taken as equal to the length EL, i.e. twice EV. The 

 formula now runs: tan « = 2 (E— L)/(E + L), where E and L stand for the 



