Sunday, November 04, 2012

Eli Points Out the Obvious Again

Well, somebunny has to do it.

Paul Krugman today

Today’s Financial Times bears a banner headline on p.1: “US election hangs on a knife edge”. Aside from everything else, surely this gets the cliche wrong: you rest on a knife edge, don’t you? If you try to hang on one, I think you just cut off your fingers.
Being an old Rabett, Eli pointed out that
the knife's edge refers to an old fashioned weighing balance where the two pans are supported by a beam and the "knife's edge" is the fulcrum point.
If you look at pictures of old balances the knife edge is in the middle.


the knife edge is the little triangular thing supporting the beam at the top of the central pillar or you could dip into the tool chest for some threaded rod and single blade razors.  You can find the fancier double pan balances in antique stores or professors' offices (Eli has two).

An interesting version is the Mettler subtractive balance (you can still find some in labs), where the weights were rings that could be lifted off the beam by an arrangement of gears and levers (11).  The counterweight (3) was equal to the sum of the weights of all the rings that hung from the beam.  The knife edges are shown in blue, one supporting the whole beam and the other the pan and rings (near 7)


So, what do we use today?  Electronic scales (this is like telling a gunny sergeant that a rifle is a gun, but sad to say it is true) measure the change in resistance of a strain gauge load cell, accurate, inexpensive (relatively) but not elegant


26 comments:

David B. Benson said...

Simplicity is elegant.

Rattus Norvegicus said...

Used Mettler balances in Chem lab more years ago than I want to mention.

John said...

Congratulations! Eli corrects a Nobel laureate. Hmmmmm....that's a plenty smart bunny!
Does Paul Krugman know about this??

Anonymous said...

I think that I want to drag Eli into my burrow.

I've always had a compulsive fascination for accurate balances that don't rely on electrickery, having cut my kit-teeth on them, but sadly getting a hold of any in my corner of the meadow is nigh on impossible. I have to go look at the ones now sheltered behind glass for my fix of sophisticated analogue technology.


Bernard J. Hyphen-Anonymous XVII, Esq.

Russell said...

Far from being sharp as a knife , which would make it prone to chip, " the little trianguar thing " is a carefully polished bit of lapidary work, generally agate , whose radiused edge rocks against an optically flat agate plate with little more friction than a jeweled watch bearing.

The razor edge to razor edge gizmo illustrated suffers from nearly infinite contact pressure at the points of contact, so weighing anything more massive than a penny invites nicking of the steel blades and concomitant loss of sensitivity and precision.

To avoid the wear and tear of grinding dust particles, which are often quartz, the really serious analytical balances of yore offered synthetic sapphire triangles instead of agate.

Sou said...

I'm always mixing up idioms so I have a tiny bit of sympathy with the person who wrote the headline in the Fin Times.

I'm thinking they mixed up 'hang in the balance' with 'resting on a knife edge'.

Now the question is, what kind of balance does the 'hang in the balance' refer to? It's quite likely to be the old balance with two pans and the knife edge in the middle, don't you think?

Lionel A said...

Ah! The old 'chemist's balance' much used during chemistry classes and then later for a very different purpose.

This was to weigh out the correct amount of micro-balloon powder made of tiny epoxy hollow spheres (a paper coffee cup half full would be emptied if one sneezed within a couple of yards range) to be stirred into an epoxy resin so as to make the filler for repair or modification of the epoxy GRP honeycomb filled equipment shelves of Lynx generation helicopters.

Now you always wanted to know that didn't you.

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J Bowers said...

That's nice of Gurwinder Signh, who can't even spell his own name right ;)

toto said...

J Bowers: I understand that Signh is a very popular name among members of the dyslexSikh faith.

EliRabett said...

Damn it, now Eli has to leave the spam.

J Bowers said...

@ toto, 10/10 very quick :) But maybe he's Welsh?

Anonymous said...

What would really surprise me is if Krugman actually knew about such things as that balance --and other things scientific.

When Gore was running against Bush, Krugman criticized Gore (in a piece called "Algorithms") for quoting scientists who study chaos theory.

Krugman referred to them as "pop" scientists and to the science of complexity as "pop science."

"Does anyone know what happened to chaos? It would be unfortunate if the already worrying faddishness of science were to receive a presidential seal of approval.
I also have a more specific worry: that a President Gore would give undue credence to the views of his favorite pop science heroes and their friends. Occasionally, I have a nightmarish vision in which the Santa Fe Institute, that temple of "complexity theory" (whose heavy hitters include Bak, biologist Stuart Kauffman and, yes, economist Brian Arthur) actually starts having direct input into major policy decisions. Now that would be scary."



And that was actually back before Krugman got the "Knowitall Prize".

Krugman might be surprised to hear that "chaos" and "complexity theory" are still very much with us and still highly relevant to complex systems (among them climate and weather)

Krugman gave a synopsis of the above piece:
"SYNOPSIS: Gore's disappointing lack of Economic and Scientific bases are a little frightening."

Krugman was frightened of real complexity scientists and that the next President might consult with them...

And then we got Bush and enough "chaos" (in the pop science sense) to last several lifetimes (to say nothing of the Rumsfeld Uncertainty Principle: "We know where they [Iraq's WMD] are. They're in the area around Tikrit and Baghdad and east, west, south, and north somewhat...")

~@:>




guthrie said...

I've got a Mettler PM4000 as my kitchen scales. I sometimes boast about having the most accurate kitchen scales in the country, although I really aught to get some proper weights for checking them.
I got them from the place I used to work after they upgraded to dustproof scales. Oddly enough conductive carbon dust causes problems with scale displays.

EliRabett said...

Hmm about all it could do is take out the lamp. Try substituting a while LED.

Aaron said...

I have seen nomads use a brass bar with notches along its bottom and a hook at one end as a scale for trade.

A basket or bag was hung from the hook, and a belt knife used to support the bar. Then, the trade goods were added and knife moved to a notch so that the bar again balanced. The number of notches the knife is moved represents the weight of the trade goods. It is one piece, simple, durable, and everyone working with pack animals carries a knife or two. It worked in a world where salt was carried in wool bags on camels or yaks.

Jeffrey Davis said...

I suspect that they were mis-remembering Brando's portentous line from Apocalypse Now: "I watched a snail [static] crawl along the edge [static] of a straight razor."

guthrie said...

Yup, that's right, the display shorted out. It was much easier to get QC to persuade the management that a nice dustproof one that didn't stop displaying the weight was a better idea, rather than have someone guddle about inside the case. It was slowly deteriorating with all the poor conditions though, and come to think of it got replaced when it appeared to stop working altogether and they stole one of my balances for the job
.
Once I got it home I took the casing off and blew the dust out, after which it worked okay.

Aaron, that sort of balance beam was in use in Europe into I think at least the post medieval period. What isn't so surprising is how important honest weights were for many centuries. Fiddle the weights and you could make extra profit from your customers, hence public weighing booths and official inspections.
Hmmm, such practises seem rather similar to denialists screeds these days.

EliRabett said...

The funny thing is that there is nothing beyond a switch and a lamp that is electrical inside these things. If you look at the picture the light path is shown in yellow. Near balance it passes through the lens/reticle at the far right and onto the screen.

Eli used to fix these things in five seconds to amaze the organikers. They are electrically primative and mechanically awesome.

Russell said...

"I have seen nomads use a brass bar with notches along its bottom and a hook at one end as a scale for trade. "

That hook on the end of larger steelyards , brass or iron, is there to facilitate the weighing of former yaks and such.

willard said...

Perhaps Krugman is more empathic than Eli:

http://www.sciencedaily.com/releases/2012/10/121030161416.htm

EliRabett said...

Ms. Rabett demurrs.

carrot eater said...

Leave the spam, but remove the links.

EliRabett said...

You go with the Blogger you got, not the Blogger you need. AFAEK there is no way for him to do thia

Anonymous said...

Well color me stoopid, that is why they call me "Hey Stoopid".

Hmmm, ah so all the Republican paid head in posterior denialati clowns are calling it a cliff hanger election on a knifes edge, are they.

Well pure fictional claims of complete nonsense , sure do have a price.

Mean while, back in the real world of numbers and reality, the odds are definitely not with Mitt "Teflon kill all the middle class" Romney.

I usually find that Nate Silverman, is pretty accurate in his past forecasts as his latest post in the New York Times shows: http://fivethirtyeight.blogs.nytimes.com/

Oh well, when you live, breathe and propagate "Republican Propaganda", you truly do stick your head up your posterior.

Such is life.

J Bowers said...

The Guardian's electoral votes numbers at the top are behind most, but the state updates you can hover over seem to be ahead of most.

http://www.guardian.co.uk/world/us-elections-2012/results/president