The choice of which type of electricity is called "positive" and which "negative" was made around 1750 by Ben Franklin, early American scientist and man of many talents. Franklin studied static electricity, produced by rubbing glass, amber, sulfur etc. with fur or dry cloth. ... Later, when electric batteries were discovered, scientists naturally assigned the direction of the flow of current to be from (+) to (-). ... Exploration" home page (index) Glossary . Official GSFC Home Page .. ...

Rhea . ... Rhea is an icy body with a density of 1.33 gm/cm 3 . The low density indicates that it is composed of a rocky core taking up less than one-third of the moon's mass, with the rest composed of water-ice. ... Rhea is heavily cratered with bright whispy markings. ... The second area, in parts of the polar and equatorial regions, has craters under 40 kilometers (25 miles) in diameter. ... Orbital period (days) . ... Credit: Calvin J. Hamilton) . ... Copyright ї 1997 by Calvin J. Hamilton . ...

... The motion of energetic ions and electrons through space is strongly constrained by the local magnetic field. The basic mode is rotation around magnetic field lines, while at the same time sliding along those lines, giving the particles a spiral trajectory. On typical field lines, attached to the Earth at both ends, such motion would soon lead the particles into the atmosphere, where they would collide and lose their energy. ... In this way the Earth holds on to its radiation belts. ...

Cosmic Research, Vol. 42, No. 5, 2004, pp. 435­488. Translated from Kosmicheskie Issledovaniya, Vol. 42, No. 5, 2004, pp. 453­508. Original Russian Text Copyright © 2004 by Veselovsky, Panasyuk, Avdyushin, Bazilevskaya, Belov, Bogachev, Bogod, Bogomolov, Bothmer, Boyarchuk, Vashenyuk, Vlasov, Gnezdilov, Gorgutsa, Grechnev, Denisov, Dmitriev, Dryer, Yermolaev, Eroshenko, Zherebtsov, Zhitnik, Zhukov, Zastenker, Zelenyi, Zeldovich, Ivanov-Kholodnyi, Ignat'ev, Ishkov, Kolomiytsev, Krasheninnikov, Kudela,