5S Dr. A. D. Waller. Various Inclinatidns of the 



geometrically the theoretical values of the first ventricular spike Vi in all 

 leads at all values of the axial angle a. 



The quadrilateral figure (fig. 5) EMLF, in which CM = £(LR) and LR = CF, 

 so that cot \ the vertical angle at M = 1, and cot \ the vertical angle at F = 2, 

 represents at its points the leading-off points mouth, hands, and feet. It 

 is pinned by its centre to the centre of a field ruled in parallel (equi- 

 potential) lines ; each division in this figure represents 1 x 10 -4 volt, so that 

 10 divisions are equivalent to 1 millivolt. Lines at right angles to the equi- 

 potential lines (not drawn) would represent lines of force ; the arrow CC 

 through the centre of the field represents the current-axis, the line 00 at 

 right angles to CC represents the equator. 



The figure and the field can he rotated in relation to each other round the 

 centre C, so that the current-axis CC is placed at any given angle from the 

 vertical. The figure being weighted so as to remain vertical, the field when 

 tilted gives any desired inclination of the current-axis, and the points 

 R, M, L, F, occupy positions upon the field that indicate directly the potential 

 differences between them, i.e., in the different leads. Thus, e.g., if the current- 

 axis is inclined 30° the values in relation to of the four points R, M, L, F, 

 will be respectively + 2 - 5, + 4rT, — 2-5 and — 8 - 6 above and below zero, and 

 the potential differences in the various leads will be given by the differences 

 of level between various pairs of points, as follows : — 



Current-axis = 



30° with vertical (as 



in fig. 



!)• 



MR (right superior) 



43-25 = 



18 x 10~ 5 volt 



ML (left superior) . 



43 + 25 = 



68 



)) 



RL (transverse) . , . 



25 + 25 = 



50 





RF (right inferior) 



86 + 25 - 



111 



jj 



LF (left inferior) 



86-25 - 



61 



JJ 



MF (longitudinal) 



86+43 - 



129 



)) 



Obviously as regards the two sides of the body, MR and LF are relatively 

 " weak " leads, ML and RF are relatively " strong " leads. Similarly the 

 potential difference in the several leads can be determined for any value 

 of a by pricking off the positions of the points M, R, L, F, and measuring off 

 the differences of level between pairs of points. It will be realised at once 

 that with high values of a the direction of the weak leads is reversed — 

 e.g. at 80° the right superior potential difference is seen to be —40 and the 

 left inferior potential difference —32. At 90° both weak leads = —50 and 

 both the strong leads = +50. 



Plotted out upon squared paper the values thus obtained give the curves 

 represented in fig. 6, which are obviously sinusoidal curves, most obviously 



