The moon displayed to him her mountain-ranges and her glens, her
continents and her highlands, now lying in darkness, now brilliant with
sunshine, and undergoing all those variations of light and shadow which
the surface of our own globe presents to the alpine traveller or to the
aeronaut. The four satellites of Jupiter illuminating their planet, and
suffering eclipses in his shadow, like our own moon; the spots on the
sun’s disc, proving his rotation round his axis in twenty-five days;
the crescent phases of Venus, and the triple form or the imperfectly
developed ring of Saturn,--were the other discoveries in the solar
system which rewarded the diligence of Galileo. In the starry heavens,
too, thousands of new worlds were discovered by his telescope; and the
Pleiades alone, which to the unassisted eye exhibit only _seven_ stars,
displayed to Galileo no fewer than _forty_.--_North-British Review_,
No. 3.
The first telescope “the starry Galileo” constructed with a leaden
tube a few inches long, with a spectacle-glass, one convex and one
concave, at each of its extremities. It magnified three times.
Telescopes were made in London in February 1610, a year after
Galileo had completed his own (Rigaud, _On Harriot’s Papers_,
1833). They were at first called _cylinders_. The telescopes which
Galileo constructed, and others of which he made use for observing
Jupiter’s satellites, the phases of Venus, and the solar spots,
possessed the gradually-increasing powers of magnifying four,
seven, and thirty-two linear diameters; but they never had a higher
power.--Arago, in the _Annuaire_ for 1842.
Clock-work is now applied to the equatorial telescope, so as to
allow the observer to follow the course of any star, comet, or
planet he may wish to observe continuously, without using his hands
for the mechanical motion of the instrument.