Semicubical telescopes pointing in the vertical direction and inclined cubical telescopes pointing in the east and north directions have been employed to measure the cosmic-ray daily variation at an underground site in London. Although the statistical accuracy of the measured daily variations is not very high, there are strong indications that during 1965, which was the year of maximum cosmic-ray flux associated with the last solar minimum, tire upper limiting rigidity of the corotation anisotropy (with time of maximum at 1800 h) was reduced to such low values that a Compton–Getting effect due to the motion of the earth around the sun became observable. Also, the atmospheric contribution to the measured solar daily variations appears to be very small. There is no evidence for an enhancement of the observable sidereal daily variation associated with the lowering of the upper limiting rigidity of the corotation anisotropy.
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