A magnetic effect was a mysterious universe-wide disturbance that caused what was otherwise described as a cosmic "winking out" phenomenon. This event was first encountered by the Federation when it was determined that such a disturbance took place twice on an uncharted iron-silica planet discovered by the USS Enterprise in 2267.
The localized results of the magnetic effect included what Enterprise science officer Spock described as "totally unbelievable", stating that "for a split second each time, everything within range of our instruments seemed on the verge of winking out." Clarifying the matter, Spock stated that "the entire magnetic field in this solar system simply blinked. The planet below, the mass of which we're measuring, attained zero gravity" or in simpler terms: "non-existence."
The wider scope of the magnetic effect was described by Starfleet Commodore Barstow, who stated that "it occurred in every quadrant of the galaxy and far beyond. Complete disruption of normal magnetic and gravimetric fields, time warp distortion, possible radiation variations." At the time, Starfleet was unable to determine if it was natural phenomena or mechanically created, and if the latter, Barstow warned of a prelude to a possible invasion. In anticipation of such an event, Barstow evacuated all Starfleet units and personnel within 100 parsecs of the epicenter.
It was eventually determined by Enterprise Captain James T. Kirk, and confirmed by anti-Lazarus that the phenomenon was created by Lazarus when he opened a negative magnetic corridor causing a so-called "rip in the universe". (TOS: "The Alternative Factor")