objects with their usual
distinctness. Fabricius speaks of observing the sun by admitting
his rays through a small _hole_ into a dark room, and receiving his
image on paper; but he says nothing about a lens or a telescope
being applied to the hole; and he does not say that he saw the
spots of the sun in this way. Harriot also viewed the solar spots
when the sun was near the horizon, or was visible through "thick
layer and thin cloudes," or through thin mist. On December 21,
1611, at a quarter past 2 P.M., he observed the spots when the sky
was perfectly clear, but his "sight was after dim for an houre."

Scheiner, in his "Appelles post Tabulam," describes four different
ways of viewing the spots; one of which is by the _interposition of
blue or green glasses_. His first method was to observe the sun
near the horizon; the second was to view him through a transparent
cloud; the third was to look at him through his telescope with a
blue or a green glass of a proper thickness, and plane on both
sides, or to use a thin blue glass when the sun was covered with a
thin vapour or cloud; and the fourth method was to begin and
observe the sun at his margin, till the eye gradually reached the
middle of his disc.

On the publication of Scheiner's letters, Velser transmitted a copy of
them to his friend Galileo, with the request that he would favour him
with his opinion of the new phenomena. After some delay, Galileo
addressed three letters to Velser, in which he combated the opinions of
Scheiner on the cause of the spots. The first of these letters was dated
the 4th of May 1612;[23] but though the controversy was carried on in
the language of mutual respect and esteem, it put an end to the
friendship which had existed between the two astronomers. In these
letters Galileo showed that the spots often dispersed like vapours or
clouds; that they sometimes had a duration of only one or two days, and
at other times of thirty or forty days; that they contracted in their
breadth when they approached the sun's limb, without any diminution of
their length; that they describe circles parallel to each other; that
the monthly rotation of the sun again brings the same spots into view;
and that they are seldom seen at a greater distance than 30 deg. from the
sun's equator. Galileo likewise discovered on the sun's disc _faculae_,
or _luculi_, as they we