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.
Magnetosphere: Ganymede is unique among moons in the Solar Systems in that it alone has a magnetosphere. The value of the moonâs permanent magnetic moment is estimated to be 1.3 x 10Â¹Â³ TÂ·mÂ³, which is three times larger than the magnetic moment of Mercury.