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Name: julie a corder
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: Around 1995

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?

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.


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."


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