Most workers of the time, on the other band, extended their investigations in many directions.

The sum total of scientific knowledge of that day had not bulked so large as to exclude the possibility that one man might master it all.

So we find a Galileo, for example, making revolutionary discoveries in astronomy, and performing fundamental experiments in various fields of physics.
Galileo's great contemporary, Kepler, was almost equally versatile, though his astronomical studies were of such pre-eminent importance that his other investigations sink into relative insignificance.

Yet he performed some notable experiments in at least one department of physics.

These experiments had to do with the refraction of light, a subject which Kepler was led to investigate, in part at least, through his interest in the telescope.
We have seen that Ptolemy in the Alexandrian time, and Alhazen, the Arab, made studies of refraction.