Ask A Scientist Mathematics Archive

Author:      julie a corder
I have been assigned a report in my 8th grade geometry class on Galileo.  I
showed my draft to my teacher, and she suggested that I include some
information on the way in which Galileo invented the sector.  I have looked
in many encyclopedias and dictionaries, but all I can find are definitions
of the word sector.  Could anyone give me some info or suggestions that
could help my paper?

Response #:  1 of 2
Author:      tee
Julie, may I suggest you recheck the assignment.  The sector of a circle or
a sphere has been used in geometry in ancient greek mathematics.  There does
not seem to be any possibility of support for its invention by Galileo. 
Perhaps some other word was intended although in briefly searching our
library for information, I could not find anything as an alternative that is
close to sector.

Response #:  2 of 2
Author:      rcwinther
She knows whereof she speaks.  "Sector" was a later name for an instrument
Galileo invented around 1596, which he called a "geometrical and military
compass".  I have found reference to it in several books on Galileo in Iowa
State University's library.  Some books refer to it only as "military
compass," not using the word "sector" at all (perhaps to avoid confusion
with a similar instrument called a sector invented by Thomas Hood in 1598).
Most only mention it (e.g., he had it manufactured and sold it at a profit
to help support himself, also gave lessons in its usage; and successfully
pursued legal action against someone who tried to plagiarize it).  A couple
of books go into some detail, and one has a pretty decent photo of this
instrument.  These are: "Galileo at Work" by Stillman Drake, and "Galileo -
His Life and Work" by J. J. Fahie.
     Galileo started by combining two instruments invented by Tartaglia:  an
elevation gauge for cannons, and an instrument called a squadra for estimat-
ing the distance and height of a target.  In addition, he inscribed various
scales on it so that it could be used for solving many sorts of problems;
Drake (in the book cited above) speaks of it as "the first modern calculat-
ing instrument applicable to practical mathematical problems of every kind."