There used to be a Radio Show “You asked for it” which dealt with things we only had a fuzzy idea about. I feel I’m back there.
It was the experimental scientists who saw the need for standards in their fields in part because they recognized the advantages of being able to make reproducible measurements anywhere in the world or at any time. In theory one only needs standards of Mass, Length and Time and every other quantity can then be defined in terms of these. The electricians argued for their own standards as did the thermometrists. The theory guys said that the gas thermometer could be used to measure all temperatures. The experimental guys tried and said “Nice theory, impossible practice”. Try inserting a gas thermometer in your … er ear."
Celcius came up with the scale based on the freezing point of water = 100 and it’s boiling point = 0. He divided it into 100 intervals. Then the rest of the world inverted the scale. Then they found that the freezing and boiling points were very difficult to achieve to much better than 0.02 C. Mercury in glass thermometers were favoured over alcohol in glass as nobody wanted to drink the mercury. OK there are other reasons but that’s a good one.
Back in 1927 the first International Practical Temperature scale was agreed to. A number of set points were established, including the triple point of water (ice, liquid water and water vapour all present). The scale is reviewed and revised - small changes these days - about every 20 years. Set points include the freezing points of pure metals such as silver and gold and the triple point of oxygen…
To interpolate between the set points standard reference instruments have been defined. The Platinum Resistance Thermometer is the one covering most the range of temperatures we civilians are interested in.
Yes, they can make a lasting impression! I bet any of us with memories going back to 1955 will be able to sing “Murray Mints”, “The Esso sign”, “Dairy Box”, “dum dum dum dum, Esso Blue” and so on - they wore a track in our minds!
Well at least you confirmed the original concept, and I always to invoke the “popular culture” defence! I much prefer these old-fashioned original reference points to the more accurate, more precise definitions due to more recent scientific knowledge.
So now water boils at 99.975 deg C. Hopefully it will drop a bit more in the next few years then I won’t have to wait so long before I can start drinking my mug of tea.
Similarly, the ideas about a metre being one ten millionth of the distance from the North Pole to the Equator via Paris, or being the length of a pendulum with period 2 seconds, are rather satisfactory, especially compared to it being 1/299792458 of the distance light travels in a second.
That, as well as being characterless, gives a kind of “chicken and egg” dilemma - is not a second defined as how long it takes light to travel 299792458m?
No, because a second is 1/31,536,000 of the time it takes the Earth to orbit the sun in 303 years out of every 400 (but not the other 97 years where it seems to take a little longer). No, let me think again - that was the original idea, but no doubt scientists have many times updated the definition of the second since then. Ah yes, it is now “The duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.” Yuck.
Missed a trick there didn’t I? 9192631770 would have been a good one to have in the quiz.
Yes Brian. It’s why I have my A Level / GCSE students singing the “Completing the Square” song. It is hideous, but they never forget it!
It’s also why people of a certain age can complete the three words that follows: “Don’t be mean with the beans mum…” ***** ***** ***** ; not to mention what product cleans a big carpet for only half a crown…
Ah but where and when? There will of course be a completely different boiling point of water for each SOTA summit and even that will vary slightly with the weather. High-altitude cooking - Wikipedia.
Should we record these in our summits database?
Jim
Well strange though it may seem, the modern definitions are not only more precise, they are much more reproducible and not difficult to achieve in a garage with the right of- the-shelf equipment. Try making a pendulum that can hold 1 second per day let alone 1 second per year. The practical limitations of simple definitions will soon be apparent.
You can get time from GPS which is linked to the SI second. Use someone else’s cesium beam for free.
A laser and a fringe counter allows you to measure length to a fraction of the laser wavelength. Only the kilogram is still defined by an artifact rather than constants of physics/nature. The definition of the ampere has been bypassed by special diodes that generate precise voltages when a microwave frequency is applied and a special transistor that generates precise resistances. Current from Ohms Law. NPL would be worth a visit by any physics teacher and the brighter students. (Or your local National Measurement Institute for non-UK readers)
One never quite knows if SOTA folks are being facetious, being such a broad church, but the parts for a Bath interferometer can be picked up cheap (<$30USD) from places like Surplus Shed and are growing in popularity for quantifying telescope mirror surfaces made by another kind of amateur. (The more traditional Foucault method is even cheaper to make, but less sensitive, only measuring to nanometre accuracy
