Derek – Thursday 3rd September 2019

It’s a dull autumn day. Almost all the buddleia has been cut back, and the wild flower bed has been cleared completely. I shall miss the latter. It was the most colourful area of the garden in midsummer with pink campion, blue cornflowers, yellow California poppies, bright red poppies and white wild carrot flowers. When most of the flowers had gone to seed it was a great site for wildlife: flies, bees and other insects. Gardens which are too tidy are poor hosts for minibeasts.

Having a bare, almost static garden, I thought I’d do some maths in our garden. A good place to start is the metre cube which is behind our container. It was given to us by the Olympic site, so a legacy of 2012. It contains a cubic metre of water. A cubic metre is 1000 litres, or a million millilitres. It weighs one tonne. This illustrates the simplicity of the metric system. Incidentally, a metric tonne is very close to an imperial ton which is why they are used almost interchangeably.

What is the volume of the pond? The pond is cuboid, so the formula is width x height x length. I measure these dimensions, ignoring the ledge. The dimensions are (in metres): 2.7 wide x 0.6 high x 3.4 long. This comes to 5.5 cubic metres or 5.5 times our metre cube. Which is why a shower of rain has little effect on the height of the pond. And why people with swimming pools don’t like water meters.

A large watering can holds around 10 litres. So our pond, at 5500 litres, would need 550 full cans. That’s a lot of filling, to and fro from the water barrels. But if every barrel were full, we would nowhere near fill the pond. The volume of a barrel (assuming vertical, rather than sloping sides) is height x area. I measure one of our biggest (the green one at the corner of the middle shelter) and it comes to a fifth of a cubic metre. So we would need 27.5 such barrels to fill our 5.5 cubic metre pond. The flowers would complain to the Steering Group if we dared.

I decide to measure the garden. I don’t have a long tape measure but a stretched stride of mine is close to a yard. I stride out the width of the garden, 17 yards (15.5 metres), and then the length, 48 yards (44 metres). These are rough measurements. But I am not building a house.

Now I am doing approximations, I decide to go for the big one. How high are the cranes that tower over us from the neighbouring building site? My scientific instrument of choice, well hardly a choice as I don’t have a theodolite, is a small plastic triangle from the Helix Oxford set of Mathematical Instruments. It is an isosceles right-angled triangle. This means it has two equal sides, with a longer hypotenuse between them.

The reason I am going on about this tiddly triangle is that it can be used to estimate heights. Holding it just under the eye, with the hypotenuse sloping upwards, I move back until the top and bottom of the crane align with the top and bottom of my triangle. I then pace out the distance, and that equates to the height.

I make it 57 yards (52 metres) up to the cabin and 95 yards (87 m) to the top of the crane arm. I repeat this latter measurement on different days, and have a range from 95 to 116 yards to the end of the crane arm. The reason for the discrepancy is twofold. The first is that after use the crane arm comes to rest at varying heights. The second is that this is an awfully inaccurate means of measuring height.

Enough maths. We fill the bird feeders and at one point have six sparrows on the feeder at the gate end of the pergola. For some, as yet, unknown reason sparrow numbers are rising after many years of decrease. This makes a change from the mass of British wildlife which is on the decline. The reasons are down to farming practices, climate change, loss of habitats and invasive species. All impelling reasons for the continuance of our urban oasis.

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