The 13th century Venetians glass blowers are known to have produced reading stones made of solid glass that was put into hand-held, single lens-type frames made of horn or wood. These reading stones were similar to hand-held magnifying lenses of today.
The stronger the magnetic field, the larger the magnetosphere. Some 20,000 times stronger than Earth's magnetic field, Jupiter's magnetic field creates a magnetosphere so large it begins to avert the solar wind almost 3 million kilometers before it reaches Jupiter. The magnetosphere extends so far past Jupiter it sweeps the solar wind as far as the orbit of Saturn.
Ganymede /ËÉ¡Ã¦náµ»miËd/ (Jupiter III) is the largest moon of Jupiter and in the Solar System, and the only moon known to have a magnetic field. It is the seventh satellite outward from Jupiter and third of the Galilean moons, the first group of objects discovered orbiting another planet.