4 2 2 D O C U M E N T 4 4 2 J A N U A R Y 1 9 2 7 If an observer is not attached to Earth, but is himself moving along a large circle around Earth at angular velocity ω, then a new magnetic additional-field forms from this proper motion of his, which is calculable by the formula just indicated, if for ω the value is inserted into it, and for sinβ, the value +1. The direction of is always vertical to the direction of motion. With a west–east motion, the magnetic north–south direction established by the moving observer will agree with the direction established by the terrestrial-surface observer (at least in our latitudes at technically feasible speeds). A measurement of the oscillation periods of their magnetic needles will show to both observers, how- ever, that the strength of the field measured by them differs from each other. One of them measures , the other . If one is moving from west to east, hence in the direction of the Earth’s rotation, then the observed initially becomes ever smaller at it is equal to zero, and then negative. Consequently, only when one has a linear west–east ve- locity that is larger than the one originating from the Earth’s rotation, which, at this geographic latitude ϕ, i.e., at the polar distance β, is known to be equal to , resp., , only then does a change in direction of the field (at 180°) occur. In a north–south motion, however, according to my view, measurable changes in the direction of the field already occur at technically feasible speeds. Since H and in this case are perpendicular to each other the magnetic needle of the moving observer will hence not point in the direction of H but will deviate from it by an angle α, whose size is determined by , or . Now, in an airplane, linear velocities of 30 m/sec can be comfort- ably maintained over longer distances. The ratio would then be H1 –ω1 H1 H e ω sinβ ⋅ ⋅ 30π c R ⋅ ⋅ -------------------------- - = H2 H H1 + e ω sinβ ⋅ ⋅ 30π c R ⋅ ⋅ -------------------------- - e ω1 ⋅ 30πc R ⋅ -------------------- – = = H2 ω1 ω sinβ ⋅ = 465 cosϕ ⋅ 465 sinβ ⋅ H1 tgα H1 H ------ –ω1 ω sinβ ⋅ ------------------- = = tgα –ω1 ω --------- 1 cosϕ ------------ ⋅ = ω1 ω ------