From: "Mike Lugo" Subject: Re: ruler and compass constructions Date: Wed, 5 Jan 2000 21:43:54 -0500 Newsgroups: sci.math Summary: List of Euclid's postulates The "theoretical" Greek compass was collapsible. Here are Euclid's postulates, from Heath's translation: Let the following be postulated: 1. To draw a straight line from any point to any point. 2. To produce a finite straight line continuously in a straight line. 3. To describe a circle with any center and distance. 4. That all right angles are equal to one another. 5. [Euclid's parallel postulate] So the third postulate doesn't allow for the "transfer of distances". The third proposition of Euclid proves that given only a straight-edge and a collapsible compass, we can transfer distances - so now we use collapsible compasses (compi?) rather than repeating Euclid's construction every time. -- Mike Lugo mlugo@thelabelguy.com http://www.thelabelguy.com/mike David Petry wrote in message news:YVRc4.364$z4.14802@news.uswest.net... > > spamless@Nil.nil wrote > > >David Petry wrote: > > >> you can simulate a marked > >> ruler by holding the points of the compass next to the unmarked > >> ruler. > > > >However, the greeks couldn't. You have to remember that the classical > >compass (Euclidean compass) collapses as soon as you lift it from the > >page. You cannot use it to take one one length, move the compass and > >duplicate the length > > That's news to me, and probably to a lot of others as well. I always > thought you could use the compass to draw two circles of the same > diameter. > > What did the Greek's compass look like? > > BTW, I feel silly responding to a post from someone who uses no > name other than "spamless".