Observations of micropulsations in the magnetic records at Tromsø

In an interesting paper Dr. Bruno Rolf has drawn attention to a number of giant micropulsations registered at Abisko in the period 1921–30. In one case (that of the micropulsations which occurred September 12, 1930( the curves from the Observatory of Aurora Borealis at Tromsø (latitude 69° 39′.8 north, longitude 18° 56′.88 east) are reproduced. During the pulsations of September 12, 1930, an absolute determination of the magnetic elements was taken at Tromsø. As the times of the readings on the theodolite are marked on the curves (the same system of time‐marking is used as at the observatories at Godhavn and Lovo), we were able to show that the micropulsations in declination ( D ), horizontal intensity ( H ) and vertical intensity ( V ) had a noticeable phase‐difference relative to each other.