Friday, May 27, 2016

Tooth and Claw

In springtime, either a great or lesser-spotted woodpecker came to our garden, first to  inspect our bird boxes (empty) and then to indulge his or her appetite on my experimental fillings of halved coconut shells.
We were delighted to see such an exotic bird in our small garden, rather forgetting that on a previous year, such a bird came to consume our entire brood of robin nestlings.
Anyhow, it was not only a new visitor but also one thoroughly enjoying my mix of bird food. Robins, great tits, blue tits, long tailed tits, coal tits and even dunnocks have also pecked away at it – the less acrobatic birds with difficulty.
When carrion crows perch on nearby television aerials and croak, they are looking for nestlings to eat. When they have found this food source, the poor youngsters are taken in the beak and flown up to a high perch to be torn apart and eaten. Magpies do the same, but those have been scarcer of late.
With our regular great tits deserting their annual breeding home in our nest box (probably one taken by a cat or succumbed to old age), our attention was drawn to a nearby neighbour’s nest box of blue tits. The young were about to fledge, when a woodpecker (perhaps ours) ate the lot.
How, I wondered, had the miscreant managed to raid the box without enlarging the entrance hole? It was suggested that just by creating noise and beak action near to the hole drew the young up to feed – only to become food themselves.
This, I suppose, is nature’s way of keeping the balance right between predatory creatures and their victims.
After all, if the young of every nestful of garden birds survived, there would probably not be enough territory or food to go around.
My popular bird food is pressed into half coconut shells with holes in them to attach hanging cord. The shell is then filled with the following: lamb’s kidney fat and suet fat (Atora will do) cut up. Heat this slowly in a saucepan until the fat has liquefied and can be poured into a bowl off the solid matter. In a liquidiser turn porridge and bran almost into powder form. Stir this into the warm fat as much as it will take – which is quite a lot. Now, with a wooden spoon, press this mixture into the shells to become cold and hard before hanging them in the garden out of the reach of cats.

Birds take time to become used to anything new. So before they start to enjoy your offering, a little patience might be needed.

Monday, May 23, 2016

Stirling Engines

I am no mechanic, but some aspects of machinery intrigue me. One is the Stirling engine. Why? Well, to me it is almost like perpetual motion, and it is a machine that is virtually silent and non-polluting when in operation. So silent is it that the Swedes and now others use it for submarine stealth under water where it will generate electricity to power the boat – in silence.
There are snags. Powerful machines are heavy, and they work at a constant speed. So for jobs like pumping water, making electricity, or spinning a ventilation fan, they are excellent – though not as efficient as an electric motor or the far more complicated and polluting internal combustion engine (like in a car).
Being an externally powered engine, it is free to use almost any source of heat, like the sun’s rays and from any normally wasted surplus heat (like water-cooling water), right down in scale to a nightlight or electric bulb. (I have seen a very small one work with the heat from a mug of hot coffee.)
So what is this rather odd machine?
For a beta type engine, take an enclosed metal cylinder with an external heat source at one end and vanes or other cooling method at the other. In this cylinder is a loosely-fitting piston on a rod, called a displacer. Heat one end of the cylinder and the air (or other gas) inside will expand, pushing the displacer toward the cold end, where the colder air pressure within the sealed container will shunt it back to the hot end. In the process an internal power piston will move in and out, hinged and connected to an external flywheel via a rod through a seal, also through which the displacer is hinge- connected to a different part of the flywheel’s circumference (actually at 90 degrees on the wheel).
So, apply heat to one end, spin the wheel, and off she goes – hopefully.
The colder the external air temperature the better.
It takes no skill to operate. A farmer, for instance, who lights a fire at the hot end, can pump water with a Stirling engine and go away to work knowing that the pump will work until the fire goes out, with no damage done or attention needed. Simplicity is the engine’s strength.
Ever since Robert Stirling, a Scottish minister, invented and patented his engine in 1816, there have been countless innovations, configurations and variations of the principle. Many patents have been lodged, there being continued interest in its use and development.
Above is the way I understand it, and as a layman in these matters I still sense that a certain amount of magic is also involved.

Tuesday, May 10, 2016

Clouds and Sky

When I was a boy and living in the country, my father, who was a farmer and a lover of nature, taught us children about wild birds, their eggs, their song, animals, growing things, keeping a grass tennis court absolutely free of weeds and much more. It was nature for us children to live with and appreciate. But I can not recall him telling us about clouds.
Clouds came into my life when I was accepted into the RAF in 1942 for flying training. But as facilities were full, I was told to return to civvy street and wait to be recalled.
I first took a job as a farm labourer, aware that food for our severely rationed population was of paramount importance. Then, hearing of a job as a prop swinger at an airfield (Theale) some five miles away, bicycled over and got it. (The job was swinging the propellers of Tiger Moth biplanes to start their engines.)
There was no meteorology for us then. So an instructor flew a Tiger Moth  upwind for a distance to see what weather was in store for the novice pilots who were learning to fly until reaching their first solo.
Having already been accepted for flying training in the RAF I was sometimes given the dual control trainee’s cockpit behind the pilot, where I learned to fly the aeroplane well enough, with the instructor almost as my passenger.
Clouds were important. For a learner they could be a deadly hazard. So clear skies were essential for all concerned.
We would come back, fly low over the grass airfield, and stick our thumbs up if the oncoming weather was fair. Then flying could begin.
My next meeting with clouds was when flying in America, where the meteorologist said that cumulonimbus clouds (those huge anvil-shaped ones) were very interesting clouds. “Pilots have found them so fascinating that they have flown into them and never come out again”. They are the clouds that form hailstones.
When piloting a Cornell trainer aircraft in Oklahoma, I flew into a cloud to see what it was like and in no time could have sworn that I was climbing dangerously and might spin. Then I popped out of the cloud heading vertically downward. Fortunately I was high enough to recover from the dive. This taught me, very forcefully, that when in clouds your instincts were useless and that relying on the aeroplane’s instruments was essential. - vital.
Now, when I rise each morning early, I scan the sky for some time to ascertain wind direction, birds landing (into wind), blackbirds patrolling their territorial boundaries, and swifts returning in springtime. Are the gulls coming inland from rough waves, or are they making off in a southerly direction toward calm seas? Aircraft condensation trails at altitude tell me wind direction high up and rough destinations of the aircraft creating them. 
Then I watch for cloud types, and their formation in broken or stratified form, and how they change shape and volume as they pass over. I can then have a shot at predicting the possible weather systems to come (stand with your back to the wind and the lower pressure area is always on the left).
I look at the trees, the way they are bending, the early development of catkins and the size and colour of the ensuing leaves.
As much as anything I watch airliners come in to land at Heathrow airport. I try to identify the type (difficult now that so many look rather alike). If they are in cloud and invisible when passing by on their way to runways 27 left or right, the cloud level is below 1800 feet. If still invisible on their final approach and leaving my usual field of vision, the clouds are 800 foot high or lower.

We seldom take time to look at the clouds, the sky, and the objects and creatures that inhabit the vast space above us. It is a vibrant and fascinating part of our world.