Nickel-plated slides were prepared by evaporating a nickel layer (congruent to 4000 A thick) on glass slides in the presence of a magnetic field whose lines of force were perpendicular to the surface of the slides. Such slides are called active. After being coated with a layer of bovine albumin, they could absorb a layer of antibodies 70-80 A thick. However, if the active slides before they were coated with bovine serum albumin, were submitted to a magnetic field with lines of force parallel to the surface, the layer of antibodies absorbed was only 40 A thick. They had become inactive. It has been found that slides remain active at night but that shortly after sunrise they become slowly inactivated and reach a minimum in their activity at exactly the midday period. They regain full activity at sunset. It is shown that the inactivation results from a solar radiation that can be stopped by 3.5 cm of lead. On December 13th, 1974 there was an eclipse of the sun with 65% occultation at noon (Daylight Saving Time). The activity of the slide at noon was 65% of the maximum activity (83 A) observed before sunrise. The thickness of the adsorbed layer of antibodies were 75 A instead of 63 A observed in the absence of the eclipse. The activation of the slides originates in a radiation of non-solar origin that is adsorbed by 1 can of lead.