Thursday 9 March 2017

A length of time


The young mason has given me the dimensions of the huge stone roundel in millimetres, not the feet and inches it would have been made in, and he has given the diamter as 915mm - supiciously close to 37 and a half inches. Hmm. I suspect laziness is involved.

The Spring and Summer ones which already exist have a foliate 'egg and dart' motif running around the edge, and the centres for these are divided into 30, not 32 as they would be if you began with a central cross and kept dividing it - 4, 8, 16, 32.

I spent quite a while yesterday in trying to calculate the circumference using Pi, but then did not trust the results. When you are dealing with a diameter which is as large as these things, a small fraction of error will lead to a gap between the 29th and 30th which is either far too small or far too big. So today I am buying the biggest protractor I can find, then mark the paper with a series of radials of 12 degrees. 360 divided by 30 = 12.

I do not believe that the original designer deliberately and pointlessly made his life difficult by using a clock-face division with these circles. They represent the Four Seasons, so they represent the passage of time, and the seasons are cyclical.

The generation after me were brought up using the post-revolutionary French system of measurement which is Metric, and do not understand why I insist on using Imperial when making or restoring things in the 19th, 18th or earlier centuries. They think I am an old man who is stuck in his ways, using pencils and paper when the computer CAD systems they have been trained in are so much cleaner, quicker and more 'convenient'. These days, they could run systems which divide by 12 or 360, but they do not - other than simple conversion tables to help them understand what I am talking about when I say 37 1/2 inches, not 915 millimetres.

You can only get into the head of a craftsman/artist who has been dead for a long time by using his methods and mindset. I once struggled to draw a large and acentrical volute (scroll) for a coat of arms  which was made in 1804, and I only made the breakthrough when I realised that the varying thicknesses of line which was carved into the stone directly related to how a broad-nibbed pen works when it is being drawn for the first time. The original carver used ink pens every day of his life, whereas I had ball-points and pencils. Once understood, I had the volute drawn out in minutes.

The imperial measurements set down by the ancients could be checked at any time by using astronomy, but the ancient yard would vary in length depending where you happened to check it on the Earth's lattitude. Short measure indeed? I don't like your lattitude!

So the seafarers set up the Greenwich Observatory and made a yardstick which was as impervious to damp, heat or cold as the materials would allow, then every now and then, Customs and Excise would take their own weights and measures there to verify imports which they were suspicious about.

On the other hand, the revoltionary French baulked against the old British system and took their own measurements of one degree of longitude between Paris and somewhere else, then came up with a system which was divisable by 10, making life for the computer designers that much easier. Their seconds could well be in units of 10 too, I've never bothered to check how it relates to time.

The trouble is that they got their measurements wrong, and by quite alot.


33 comments:

  1. I do not have a comment on this, other to say that you explain complicated things in such an easy way that a thick person like me can understand. I never thought I could enjoy reading technical stuff with such interest.
    Greetings Maria x

    ReplyDelete
    Replies
    1. It turns out that I don't understand it myself.

      Delete
  2. Oh Tom. As a mathematical zero, I have a whole new respect for you using Pi. I told my husband once to measure twice and cut once and his head exploded.

    ReplyDelete
    Replies
    1. I got zero for my maths O-Level. This is true.

      Delete
  3. Peter thinks in pre-decimal currency when calculating what housekeeping to give me.

    ReplyDelete
    Replies
    1. There were a couple of very old women in Canterbury who ran a bakery when I was there. They could not come to terms with decimal, so just quoted old money for cakes etc. Everyone went along with it and if you went there every day, sometimes you won and sometimes you lost, but it all balanced out in the end.

      Delete
    2. It is not unusual in this area for people to still talk in £sd.

      Delete
  4. Something is wrong 37.5 inches is 954 millimetres whereas 915 millimetres is 36.024 inches !

    ReplyDelete
    Replies
    1. Yes you and Maryanne are right Heron. If the young man had just said 36 inches - or a yard - to me, then I would not have to re-draw the bloody thing again...

      Delete
  5. Remember the fiasco that was the Hubble Telescope ? Perhaps you should/could check someone else's measurements. I just want a dishwasher to fit in a space and I've got to get the supplier and installer in to measure - just in case.

    ReplyDelete
    Replies
    1. I once donated my tape-measure to a Floridian carpenter, because he had never seen a tape with imperial on one side and metric on the other. I don't think NASA had either.

      Delete
  6. I like deciphering old codes. I used to go through my grandmother's turn of the last century pattern books, and marvel at what women could decipher from pre-standard knitting directions, hand drawn graphics and hand drawn pictures of the finished product. I found a pattern for a pair of gloves. Now, gloves are incredibly fiddly to knit, but these were intriguing, so I began knitting them, line by line of directions. The final instruction was, "if you have done this correctly, the glove will look like this," and a hand drawn picture. I not only did it correctly, I rewrote the entire pattern in current knitting language, and give it to anyone who says they can't knit gloves. They're that ingenious and simple.

    ReplyDelete
    Replies
    1. Joanne, I'm emailing you when I get in a conundrum. I have no patience to read instructions.

      Delete
    2. I like the translated Chinese instructions. At least you can laugh while you try to assemble something.

      Delete
  7. The French government may have adopted metric, but when I was first in France in the eighties my elderly neighbours still referred to gallons of liquid and pounds of solid, not a kilo or litre in sight. They were also in pre de Gaulle devaluation francs as well which could give quite a shock when enquiring the price of something.

    Metric is so inflexible a system...perhaps its proponents were those congenitally incapable of working out the price of three and seven eighths yards of material at one shilling and elevenpence farthing the yard.

    ReplyDelete
    Replies
    1. They carried on with old Francs for quite a while too.

      Delete
  8. My husband and I have done a lot of wood projects together. But when we try to divide 3/8 we always end up doing the same thing: We get out the German measuring stick. The other day we tried to figure out angles. It was not a proud moment.

    ReplyDelete
    Replies
    1. The German Measuring Stick? A euphemism, I presume? Angles? Not 'proud'?

      Delete
    2. Alles ist in Ordnung.

      Delete
    3. It is a day later and I just realized that this whole thing sounded completely wrong. I was really talking about making furniture and stair railing's and so on. Trying to divide 7/8 or 5/16 always leads us back to using centimeters and millimeters.

      Delete
  9. Halves, quarters, thirds, and sixths, will always have the advantage over just halves.

    ReplyDelete
    Replies
    1. Well they may be smaller, but there is more of them.

      Delete
  10. 915mm is a yard, Tom. That's one thing I know for sure! might make more sense then!

    ReplyDelete
    Replies
    1. Oh God - I've just checked and I believe you are right, Maryanne. I just cannot seem to cope with switching between one system and another. Damn - I am going to have to re-draw what I did yesterday...

      Delete
    2. Bummer! I spend all summer explaining how much fabric in yards American tourists are going to get in a metre etc, so I'm well used to it. Also, we sell lampshade frames and rings, all of which are made on very old jigs made in inches, and I secretly prefer inches and yards anyway. Thank goodness our illogical American neighbours who embraced the dollar cling to imperical measurement systems so we still can get rulers, graph paper etc in inches. Enjoy x

      Delete
    3. PS top tip, you hace a wonderful haverdashery place in Bath called the Makery. I recommend you pop in there and by an analog dressmaking tape measure, which has both inches and centimetres on it. Easiest onversion ever as you can see them side by side. If it cost you more than 2 quid I'm a supermodel!

      Delete
    4. pps bloody stupid acrylic finger nails from wedding are destroying my already dodgy typing, sorry for the typos. I trust it makes sense!

      Delete
  11. Nose to outstretched arm and tip of middle finger is a yard on me. If I turn my head away from the arm the distance goes metric and it is one metre. Happy to help.

    ReplyDelete