Geomagnetic tides in horizontal intensity at Huancayo

Following an introductory survey of the main features of the solar and lunar daily variations, S and L, in horizontal intensity, H , in January at Huancayo, days with conspicuous lunar influences, geomagnetic tides, are discussed. A separation of S and L on such “big‐L‐days” is attempted. Daily ranges A in H are then introduced for the study of the intensity of S and, thereby, of the solar wave‐radiation W . Up to international character‐figures C =1.1, A is found independent of changes in the solar corpuscular radiation P . Various methods for studying L are compared. Lunar semimonthly waves in the ranges A are computed and discussed in their change with season and sunspot‐cycle. In the months November to March, when L is larger than in the rest of the year, L and S increase, in their effects on A , proportionally to each other from sunspot‐minimum to sunspot‐maximum, but around June, when L is small, it does not participate in the change of S with the sunspot‐cycle. The day‐to‐day variability of S and L is studied in some detail; S and L fluctuate rather independently of each other, and the relative fluctuations of L seem to be greater than those of S. The elimination of the lunar effect A L is described; ( A − A L ) = A s is proposed as a measure for W . A more extensive summary, including some results to be described in Part II, has been published elsewhere [see 4 of “References” at end of paper].