Mangetout’s suggestion is right, and is equivalent to folding.
Would a laser beam be sufficiently close to a “perfectly straight line” or will Einstein’s theories serve to prove that the laser is not “straight” due to the effects of gravity? If that’s the case, I give up on seeking perfection.
It seems likely that the impetus to create a straight edge would have started with the invention of the spear. The first and most obvious test of a straight edge is to sight along it and make corrections by scraping. With patience, you can actually achieve a very straight edge that way, especially if you start with a good piece of straight-grained wood.
The idea of comparing at least three examples to refine straightness probably came up while spears and arrows were still the high tech application. By the time folks started working stone they probably had a pretty good idea of how to create as straight an edge as they needed for short work.
As for longer lines, folks would have thought of stretching a string pretty quickly when the need arose. I gather that’s been standard practice for dividing up the Egyptian flood plains for agriculture for a very long time. For even longer work, the establishment of sight lines is pretty evident in old works like Stonehenge. No lasers required!
As for using liquid leveling to create a flat, I’m sure that came into the arsenal of measurement too. I was taught in school that the ancient Greeks sometimes used wax tablets as “erasable” writing surfaces, so they would have known of its self-leveling tendencies. (BTW: at that scale, I think surface tension around the edges would affect flatness more than the Earth’s curvature.)
What is your definition of “straight”?
Taut string or wire suffers catenary curvature.
ManiacMan’s post is the straight dope on making one;three lines are brought to truth with each other.
Cast iron edges are used by millwrights/fitters/machinists, the best true to .0001/12" obtained by hand scraping.Practical lengths are about 8’,which will take two grown men to handle.
The only teenager in school who couldn’t get a fake ID decided he’d protest by drawing black X’s on his hands with magic markers and run around saying “I don’t need alcohol to have a good time” until he turned 21.
Ahh the 80’s. I thought the first joke was going to have to do with becoming hetero. Back to the OP, the methods we used as kids was to roll the item, then bend (like a pool cue) or get into my Dad’s tool box and use his plumb bob (weight on a string) or that purple snapping string thing that puts a line on the ground.
I though it was the first kid who decided to stop hanging out with the living dead.
(OK, you beat me to it. xXDamnYouXx!)
At times when I didn’t have a pre-built level, I’ve just filled a square glass with water. Works just fine for picture-hanging purposes.
And of course getting a vertical straight line is still done with string and a tiny piece of lead.
This only works if the surfaces are flat - if you fold a piece of bubblewrap or corrugated cardboard then the resultant edge is going to be ridged.
Bit of a contradiction there old chap.
They had less technology than us therefore their intelligence must have been less otherwise their technology would have been the equal of ours.
Or summink
No. Intelligence is the ability to problem-solve, not the amount of time you’ve had to build toys.
They didn’t have our mastery of materials and techniques specific to those materials, but those things aren’t based on our individual intelligence anyway - you’re a smart guy, chowder, but you didn’t work out how to smelt the metal you use, or make the semiconductors in your phone, etc.
Our technology is largely a result of the accumulated application of intelligence - but exactly the same kind of intelligence our ancestors had.
>Would a laser beam be sufficiently close to a “perfectly straight line” or will Einstein’s theories serve to prove that the laser is not “straight” due to the effects of gravity?
Einstein’s theories are about straight lines, more than being about whether light follows them. For example, there are distant astronomical objects such that multiple straight lines go from here to there and get pretty far apart at times. But the lines are straight.
>Taut string or wire suffers catenary curvature.
Nava’s hanging one doesn’t.
[QUOTE=Napier
>Taut string or wire suffers catenary curvature.
Nava’s hanging one doesn’t.[/QUOTE]
Touche.But we were talking edges,straight, not plumbs,bob.
Somebody up there mentioned a quartz edge, which along the same lines as muscovite. Even today muscovite is used in atomic force microscopy to produce atomically flat surfaces.
Derleth/Mangetout:
I stand corrected
What about ice? How flat would an ice surface be if the water was allowed to freeze undisturbed?
A taut line with a slight catenary curve is still straight in the vertical plane, so would make a good straightedge for a lot of situations.
Still, with all the reasonable suggestions, it seems like this one was nailed in the first response.
The first straight edge was in 1980, according to this site
Only in Z. Works fine for laying straight lines on an X-Y plane, such as a mud flat.
Depending on its size and whatnot, it might tend to heave up in the middle. I’ve seen ice cubes frozen with a one- or two-inch spike growing out of the top surface. (I forget the mechanism, it was explained in Scientific American a few years back, I think).
Thanks for the link. I was suffering from major whoosh.