Studying for nitrox class- please help

[Guy Alcala]

Actually it is probably not true that "it is sheer luck". The initial eighteenth century definition of meter is related to the radius of earth and gram is related to the mass of fresh water which makes the product of \rho(density of sea-water ~ 3% more that of freshwater) and g(acceleration due gravity) close to 10. Only contribution of the luck is the value of Gravitational constant, though it was also implicitly linked to density of earth to density of water by Cavendis' famous experiment in 1798.

Mainak

Very true. I had read a book last year (can't remember the title) describing the effort by two French scientists in the 1780-90s to measure the distance to establish the length of a meter (IIRR it was supposed to be 1/10 millionth of the distance from the equator to the pole along a meridian). The fact that this project was given the go-ahead under the monarchy but only started while the revolution unfolded made it a lot more personally dangerous than it would otherwise have been.

Of course, the problem was that as the accuracy of measurement improved it would throw the meter's length out, making the whole idea to tie the meter's length to a 'fixed' earth-based measurement somewhat utopian at best, nonsensical at worst. And one of the scientists made a mistake which introduced a small error into the calcs, but was too ashamed to admit it.

Guy

 

[cricfanSD]

Most likely that book is "The Measure of All Things - The Seven-Year Odyssey and Hidden Error That Transformed the World ". A very interesting read.

 

[Anti-Hero]

Congrats on passing your Nitrox class!

 

[Peter_C]

I will say congrats too. Now get out and put the class to use by sucking down some nitrox tanks.

I dive pretty much nothing but 32%. Recently I thought I was going to have to dive air...but Aquarius on Del Monte came through! Shoot I haven't dove air in over a year. Then again I haven't dove warm water in over a year either.

 

[Chuck Tribolet]

Actually it is probably not true that "it is sheer luck". The initial eighteenth century definition of meter is related to the radius of earth and gram is related to the mass of fresh water which makes the product of \rho(density of sea-water ~ 3% more that of freshwater) and g(acceleration due gravity) close to 10. Only contribution of the luck is the value of Gravitational constant, though it was also implicitly linked to density of earth to density of water by Cavendis' famous experiment in 1798.

It only takes one element of luck to make the whole outcome
sheer luck. For multiplication: Luck is a lot like zero and infinity:

zero*anything (except maybe infinity) = zero
infinity*anything (except maybe zero) = infinity.
luck*anything = luck.

The case in question involves multiplying luck.

The Cavendish experiment isn't relevant, and didn't measure the
gravitational constant.

 

[Guy Alcala]

Most likely that book is "The Measure of All Things - The Seven-Year Odyssey and Hidden Error That Transformed the World ". A very interesting read.

That's the one. I was re-reading "The Great Arc" at the time and went on a theme reading binge

Guy

 

[cricfanSD]

The Cavendish experiment isn't relevant, and didn't measure the
gravitational constant.

The value of g won't be 9.8 m/s^2 unless G is measured and Cavendish did exactly that. He didn't explicitly measure G but used its influence to measure the Earth's density relative to fresh water. At least that is what we were taught in Metric world. His measured value was 6.754 × 10−11 and the current measurement is 6.693 × 10−11.
IMHO using Imperial units for Scuba makes things unnecessarily complicated and for people like me who had never used any of these units before coming to USA it was hard in the beginning. I think I still convert to metric, calculate and convert back sub consciously.