The same author asserts that such a “catastrophe” is the true explanation of Mantell’s death (p. 33). Supposedly objecting to his close approach, the occupants of the saucer he was chasing manipulated some of the lines of force until they crossed in front of Mantell; the resulting surge of power knocked the plane out of the air. Under some conditions, he adds, the crossing of the lines can produce desirable effects, such as the Aurora Borealis, when “we have magnetic lines of force that are crossing one another at or near the geographic and the magnetic poles and as a result we see those beautiful colored lights.”[IX-20, p. 141] To the physicist, these statements are an unsavory verbal hash. Lines of force cannot provide a source of power and they cannot cause explosions--they are not even real. Created merely to describe the behavior of magnetic fields, they have no more objective existence than a train of thought. By using the convenient fiction that lines of force emerge from the north magnetic pole, spread apart as they flow around the earth, and then crowd close together again as they enter the south magnetic pole, the physicist is able to map observed variations in the earth’s magnetic field. In a similar way the geographer uses contour lines to map high and low areas on the earth’s surface. A spacecraft could not propel itself by hitching to magnetic lines of force any more than a man could travel from Philadelphia to Peru by sliding down the 75th line of longitude. The more sophisticated students of UFO behavior do not propose magnetic lines of force as a source of power. In fact they skip lightly over the awkward question of how the saucers are propelled and vaguely assert that extraterrestrial vehicles obtain energy (apparently without doing equivalent work) by somehow plugging in to the cosmic rays and magnetic fields that exist in space. Thus having access to unlimited power, a saucer supposedly draws on E-M forces to create and enclose itself in a kind of cocoon of artificial gravity. This G-field cuts off the attraction of the earth and other heavenly bodies, enables the saucer to attract or repel any approaching object, and allows it to travel almost as fast as light without suffering an increase in mass or a transformation into energy[IX-18]. _The G-Field Myth_ To explain the alleged properties and behavior of flying saucers, a variety of speculations have been published on the nature and operation of the G-field[IX-18, IX-19, IX-21]. In the physicist’s view, most of these ideas belong more to the realm of magic than of science but we shall summarize them briefly, with a few parenthetical comments.