apart by a wedge to remove arrow
heads. Fractured bones were splinted or encased in plaster.
Dislocations were remedied. Hernias were trussed. Bladder stones
blocking urination were pushed back into the bladder or removed
through an artificial opening in the bladder. Surgery was
performed by butchers, blacksmiths, and barbers.

Roger Bacon, an Oxford master, began the science of physics. He
read Arab writers on the source of light rays being from the object
seen, the nature of refraction and reflection of light, and the
properties of lenses. He studied the radiation of light and heat.
He studied angles of reflection in plane, spherical, cylindrical,
and conical mirrors, in both their concave and convex aspects. He
did experiments in refraction in different media, e.g. air, water,
and glass, and knew that the human cornea refracted light, and
that the human eye lens was doubly convex. He comprehended the
magnifying power of convex lenses and conceptualized the
combination of lenses which would increase the power of vision by
magnification. He realized that rays of light pass so much faster
than those of sound or smell that the time is imperceptible to
humans. He knew that rays of heat and sound penetrate all matter
without our awareness and that opaque bodies offered resistance to
passage of light rays. He knew the power of parabolic concave
mirrors to cause parallel rays to converge after reflection to a
focus and knew that a mirror could be produced that would start a
fire at a fixed distance. These insights made it possible for
jewelers and weavers to use lenses to view their work instead of
glass globes full of water, which distorted all but the center of
the image: "spherical aberration". The lens, whose opposite
surfaces were sections of spheres, took the place of the
central parts of the globe over the image.

He knew about magnetic poles attracting, if different and
repelling, if the same, and the relation of magnets' poles to
those of the heavens and earth. He calculated the circumference of
the world and the latitude and longitude of terrestrial positions.
He foresaw sailing around the world.

Bacon began the science of chemistry when he took the empirical
knowledge as to a few metals and their oxides and some of the
principal alkalis, acids, and salts to the abstract level of
metals as compound bodies the elements of which might be separated
and recomposed and changed among the states of solid, liquid, an