Joined: 22 Mar 2005 Posts: 4840 Location: G-Spot, Colorado
Posted: Thu Mar 29, 2012 6:17 pm Post subject:
It seems like other factors (cream, coffee temp, air temp, humidity, air or coffee turbulence, etc) would have as much of more influence on the bubbles. _________________ There cannot be pleasure without pain. -Skerik
Matt
Last edited by MattB on Thu Mar 29, 2012 8:17 pm; edited 1 time in total
it would have to do with the concavity(convexity) of the coffee surface during high(low) pressure. The bubbles would tend to move down slope. This must assume some delicate balance between surface tension (or capillary action) along the edges of the cup and the ambient atmospheric pressure--- e.g. a meniscus.If we assume that the height of the coffee in the cup is constant along the edges due to surface tension on all days regardless of pressure, then on days with higher than average pressure you might expect the water surface to bow down towards the middle... and the opposite on low pressure days. So bubbles on the edges would = potentially stormy weather.
In other words the water surface acts like a diaphragm, which is in fact how many high precision barometers function.
All that said I think its a load of sh*t. What constitutes high pressure vs. low pressure? If the meniscus is naturally inclined to be concave, just how much of an decrease in pressure would be required to make it convex... I'm sure someone has calculated it... but I'd rather just drink the coffee.
Joined: 06 Dec 2004 Posts: 3189 Location: Betwixt the Silvers and Saint Johns
Posted: Thu Mar 29, 2012 8:20 pm Post subject:
MWO wrote:
All that said I think its a load of sh*t. What constitutes high pressure vs. low pressure? If the meniscus is naturally inclined to be concave, just how much of an decrease in pressure would be required to make it convex... I'm sure someone has calculated it... but I'd rather just drink the coffee.
plus it's all about rising and falling pressure, not the current pressure, in terms of forecasting- so you'd have to compare bubbles over time even if that did work, like how you compare a baramoter hand to the set wand (or whatever it's called) _________________ Reluctant enthusiast, part-time crusader, half-hearted fanatic
Joined: 26 Mar 2008 Posts: 623 Location: Easthampton, MA
Posted: Thu Mar 29, 2012 9:38 pm Post subject:
Tele Till You're Smelly wrote:
plus it's all about rising and falling pressure, not the current pressure, in terms of forecasting- so you'd have to compare bubbles over time even if that did work, like how you compare a baramoter hand to the set wand (or whatever it's called)
Correct. Rates of change (be it with respect to time or position) are far more important than absolute pressure or temperature.
... I've gone all ChemE on you guys, haven't I? _________________ "uhh Pete, your NTNs are NTNing." - Sawyer
Joined: 06 Dec 2004 Posts: 6403 Location: with flavor crystals
Posted: Fri Mar 30, 2012 1:28 pm Post subject:
I can tell how windy it is by looking into the toilet bowl at work.
I swear to god....
Our village water comes from a water tower and when it's blowing hard out, the water 'surges' in the plumbing. It's barely noticable, but it really does happen.
Joined: 06 Dec 2004 Posts: 13192 Location: People's Republic
Posted: Fri Mar 30, 2012 1:48 pm Post subject:
Mark Twain wrote:
CHAPTER XXXVIII.
WE went into camp on that wild spot to which that ram had brought us. The men were greatly fatigued. Their conviction that we were lost was forgotten in the cheer of a good supper, and before the reaction had a chance to set in, I loaded them up with paregoric and put them to bed.
Next morning I was considering in my mind our desperate situation and trying to think of a remedy, when Harris came to me with a Baedeker map which showed conclusively that the mountain we were on was still in Switzerland,—yes, every part of it was in Switzerland. So we were not lost, after all. This was an immense relief: it lifted the weight of two such mountains from my breast. I immediately had the news disseminated and the map exhibited. The effect was wonderful. As soon as the men saw with their own eyes that they knew where they were, and that it was only the summit that was lost and not themselves, they cheered up instantly and said with one accord, let the summit take care of itself, they were not interested in its troubles.
Our distresses being at an end, I now determined to rest the men in camp and give the scientific department of the Expedition a chance. First, I made a barometric observation, to get our altitude, but I could not perceive that there was any result. I knew, by my scientific reading, that either thermometers or barometers ought to be boiled, to make them accurate; I did not know which it was, so I boiled both. There was still no result; so I examined these instruments and discovered that they possessed radical blemishes: the barometer had no hand but the brass pointer and the ball of the thermometer was stuffed with tin foil. I might have boiled those things to rags, and never found out anything.
I hunted up another barometer; it was new and perfect. I boiled it half an hour in a pot of bean soup which the cooks were making. The result was unexpected: the instrument was not affected at all, but there was such a strong barometer taste to the soup that the head cook, who was a most conscientious person, changed its name in the bill of fare.
The dish was so greatly liked by all, that I ordered the cook to have barometer soup every day. It was believed that the barometer might eventually be injured, but I did not care for that. I had demonstrated to my satisfaction that it could not tell how high a mountain was, therefore I had no real use for it. Changes of the weather I could take care of without it; I did not wish to know when the weather was going to be good, what I wanted to know was when it was going to be bad, and this I could find out from Harris's corns. Harris had had his corns tested and regulated at the government observatory in Heidelberg, and one could depend upon them with confidence. So I transferred the new barometer to the cooking department, to be used for the official mess. It was found that even a pretty fair article of soup could be made with the defective barometer; so I allowed that one to be transferred to the subordinate messes.
I next boiled the thermometer, and got a most excellent result; the mercury went up to about 200° Farenheit. In the opinion of the other scientists of the Expedition, this seemed to indicate that we had attained the extraordinary altitude of 200,000 feet above sea level. Science places the line of eternal snow at about 10,000 feet above sea level. There was no snow where we were, consequently it was proven that the eternal snow line ceases somewhere above the 10,000 foot level and does not begin any more. This was an interesting fact, and one which had not been observed by any observer before. It was as valuable as interesting, too, since it would open up the deserted summits of the highest Alps to population and agriculture. It was a proud thing to be where we were, yet it caused us a pang to reflect that but for that ram we might just as well have been 200,000 feet higher.
The success of my last experiment induced me to try an experiment with my photographic apparatus. I got it out, and boiled one of my cameras, but the thing was a failure: it made the wood swell up and burst, and I could not see that the lenses were any better than they were before.
I now concluded to boil a guide. It might improve him, it could not impair his usefulness. But I was not allowed to proceed. Guides have no feeling for science, and this one would not consent to be made uncomfortable in its interest.
In the midst of my scientific work, one of those needless accidents happened which are always occurring among the ignorant and thoughtless. A porter shot at a chamois and missed it and crippled the Latinist. This was not a serious matter to me, for a Latinist's duties are as well performed on crutches as otherwise,—but the fact remained that if the Latinist had not happened to be in the way a mule would have got that load. That would have been quite another matter, for when it comes down to a question of value there is a palpable difference between a Latinist and a mule. I could not depend on having a Latinist in the right place every time; so, to make things safe, I ordered that in future the chamois must not be hunted within the limits of the camp with any other weapon than the forefinger.
My nerves had hardly grown quiet after this affair when they got another shake-up,—one which utterly unmanned me for a moment: a rumor swept suddenly through the camp that one of the barkeepers had fallen over a precipice!
However, it turned out that it was only a chaplain. I had laid in an extra force of chaplains, purposely to be prepared for emergencies like this, but by some unaccountable oversight had come away rather short-handed in the matter of barkeepers.
_________________ that sounds like a sure-fire way to get bitch-slapped by devil's club -- dschane
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Positively riveting!
