of the De Bilt Observatory, makes a very desirable comparison, chiefly for the year !915, of measures of terrestrial magnetic activity proposed by various investigators. For the various measures, designated below, the following symbols are used here' D, magnetic declination; H, horizontal intensity; Z, vertical intensity; R, absolute diurnal range, ov difference between extreme daily values of element considered; and A, diurnal range of hourly values (mean value over 60-minute interval).

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... y x A h _-_ A x Ah q-d 2 2 2 R 2 ½• Z(RD+ R,t+ R z )=z Z(A D -Jr-A H q-A Z) = Z A lg(R D + R H q-Rz) = I R e. HR H Z(Mag. Char. Nos.) • Z C Proposer and Institution Bidlingmaier, Wilhelmshaven Observatory Chree, Kew Observatory Schmidt, Potsdam Observatory