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Electron band structure in germanium, my ass (2001)

(pages.cs.wisc.edu)
896 points tux3 | 12 comments | 01 Apr 25 12:25 UTC | HN request time: 1.41s | source | bottom
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shadowgovt ◴[01 Apr 25 15:08 UTC] No.43547706[source]▶
This reminds me of how the Fahrenheit scale came about.

For all its flaws, Fahrenheit was based on some good ideas and firmly grounded in what you could easily measure in the 1720s. A brine solution and body heat are two things you can measure without risking burning or freezing the observer. Even the gradations were intentional: in the original scale, the reference temperatures mapped to 32 and 96, and since those are 64 units apart, you could mark the rest of the thermometer with a bit of string and some halving geometry. Marking a Celsius scale from 0 to 100 accurately? Hope you have a good pair of calipers to divide a range into five evenly-spaced divisions...

Nowadays, we have machines capable of doing proper calibration of such mundane temperature ranges to far higher accuracy than the needle or alcohol-mix can even show, but back then, when scientists had to craft their own thermometers? Ease of manufacture mattered a lot.

replies(2): >>43548657 #>>43552359 #
1. oddmiral ◴[01 Apr 25 16:25 UTC] No.43548657[source]▶
100 + 28 degrees are not harder to mark than 64, and then aim 0 and 100 properly. :-/
replies(1): >>43548935 #
2. shadowgovt ◴[01 Apr 25 16:48 UTC] No.43548935[source]▶
What would be the process to do that? To aim 0 and 100 properly, you'd need a tool to calculate a 100:28 (25:7) ratio on an arbitrary distance, wouldn't you?

One can build such a tool, but it's not a doubled-over piece of string.

replies(2): >>43549542 #>>43550334 #
3. fluoridation ◴[01 Apr 25 17:40 UTC] No.43549542[source]▶
Surely you can simply use a ruler and rotate it away from the parallel to achieve any arbitrary scale, right?
replies(1): >>43549779 #
4. shadowgovt ◴[01 Apr 25 18:08 UTC] No.43549779{3}[source]▶
If you happen to have a good ruler (again, 1720s... Those also cost money or time to make). A ruler and a T-square would work. But still, it's more complicated and requires a lot more bench to secure things in place at angles than folding a piece of string in half.
replies(1): >>43550105 #
5. fluoridation ◴[01 Apr 25 18:41 UTC] No.43550105{4}[source]▶
Well... Yeah. It costs money and/or time to make things. That's as much true now as it was back then, but I don't think a ruler would have been particularly difficult to make, even with 18th century technology.
replies(1): >>43552341 #
6. oddmiral ◴[01 Apr 25 19:09 UTC] No.43550334[source]▶
Make marks on the thermometer at 0 and 100 degrees C, then project light from a candle to a wall to see these marks with say 5x magnification. Now project marks from the 128 mark ruler to the same wall and align marks from both, then place marks on the thermometer with 5x better accuracy.
replies(2): >>43550503 #>>43552346 #
7. shadowgovt ◴[01 Apr 25 19:28 UTC] No.43550503{3}[source]▶
Sounds doable, but again, you're comparing that approach to:

- get some string

- measure a length between your low and high points

- fold it in half

- make a mark at the halfway point of the string

- fold it in half again, etc.

No candles, projection, transparent or slotted ruler, wall, or carefully moving one's hand back and forth under projected magnification needed. Just some string.

8. ◴[01 Apr 25 23:23 UTC] No.43552341{5}[source]▶
9. timewizard ◴[01 Apr 25 23:24 UTC] No.43552346{3}[source]▶
A candle is an exceptionally unstable light source. The flame continually moves location as it burns. Any air currents in the room will disturb it and cause flame shadows to be cast. Adding magnification will just make this all worse.
replies(2): >>43553638 #>>43554086 #
10. ForOldHack ◴[02 Apr 25 04:17 UTC] No.43553638{4}[source]▶
Henry Cavindish used them to measure G. I used lasers and never got even an order of magnitude closer.
replies(1): >>43553742 #
11. timewizard ◴[02 Apr 25 04:43 UTC] No.43553742{5}[source]▶
His measurement apparatus was designed to eliminate air currents was it not? He also had a torsion balance and a vernier to make measurements of the /relative/ changes induced in the apparatus.

I don't see how you're going to use this system to effect repeatable markings on glass tubes.

12. oddmiral ◴[02 Apr 25 06:16 UTC] No.43554086{4}[source]▶
These problems are easy to solve in practice: just put the candle into a lantern.

Try it: it's easy. Use a flashlight from your phone instead of a candle, then project light to a wall, then put your palm in the front of the light.