The electrical position of the heart with reference to the electrodes used in studying its field is unknown. For reasons presented. it is more likely eccentric; hence, the equation defining the field of an eccentric dipole in a spherical medium might be useful for projected experimental studies and for better understanding of the way in which a given electrical position determines the electrode potentials. A method introduced by Helmholtz was used for deriving the desired equation. It is discussed since its concepts are of considerable importance to other electrocardiographic problems, too. The more simple mathematical example dealing with the centric dipole in the sphere is discussed. The equation for the field of the eccentric dipole is given and data based upon it are presented in numerical and map form. The Helmholtz equation for the field in the spherical conductor produced by two small spherical electrodes arbitrarily located is also presented and briefly discussed.T WO of the assumptions upon which the equilateral triangle of Einthoven is based are: (1) that the electric field generated by the heart may be regarded as not significantly different from that of a current dipole at the center of a homogeneous spherical conductor, and (2) that this origin is equidistant from the apices of the triangle defined by the standard limb leads. It is, of course, obvious that these assumptions disregard the eccentric location of the human heart, which is, at least in the geometric sense, considerably nearer the left than the right shoulder, and much farther from the junction of the left leg with the trunk than from the right shoulder. It is also much closer to the anterior than to the posterior surface of the chest. The spatial relations suggest, therefore, that its field may resemble that of an eccentric dipole more closely than that of a centric dipole. For this reason it seemed to us that the equation which defines the field of an eccentric dipole in a spherical medium might prove useful in connection with a projected experimental study of the field established by connecting electrodes placed on the precordium of the living subject, or in the heart of a cadaver, to a current source.

The acceptable zeros of the potential of the electrical fields produced by certain dipole distributions in homogeneous volume conductors is discussed. A bridge circuit is described by which a solution of the three-arm and the four-arm central terminals of Wilson may be solved for a zero of potential of the field produced by an arbitrary distribution of dipoles in a homogeneous volume conductor. An acceptable zero of potential for evaluation of the potentials in a locus on the "body" surface distant from the heart is described.

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