A sewage works can seem beautiful

DERBLUH-VAY-SAY. Part two. Why did my wife recommend I pay any price to have our French house connected to the main drains? (see Where there's muck there's mind expansion, May 12). In retrospect, the alternative hardly bears thinking about.

Access to the septic tank was via a trapdoor in the bathroom floor. The moment when the concreted cavity reached capacity was unmistakable. Time to contact the emptyist.

He arrived by tractor towing a large barrel on wheels. In turning into the adjacent alley the trailer brushed against the corner of our house causing a vent at the end of the barrel to open. Unspeakably.

A hose had to be passed through the bathroom window but was too wide for the protective bars. Why not, I suggested, widen the bars with the thingummyjig for raising a car? The emptyist's eyes widened. "Ah, un clic!" Which was a first for me.

The bars were bent slightly and the hose lowered into the unspeakability. A pump started up on the tractor. In the bathroom the emptyist's father, staring avidly, watched the level drop, reciting "Impeccable. Impeccable." - each syllable separated as if it were part of a liturgy. My wife was at this time wandering through fields probably a kilometre away.

The connection fee to the sewers was the predicted £2000. Neither of us complained.

The cost of instant pictures

No such thing as a free lunch, no such thing as an unpaid-for leap forward in technology. A digital camera removes that delay between "Click." and "Ahhh." but the price is a niggling awareness of battery inadequacy. I mentioned this to a photographer working for the local newspaper and he pointed to a lumpish box attached in some way or other to his Nikon. Even this awkward device supplied juice for no more than a day.

Yes, I scrupulously avoid long periods of screen viewing and always carry re-charged batteries. And always curse when the camera goes dead a nano-second after the Low Battery warning. Any tips?

And yet, and yet... What would a blog or a website be without pictures? In colour too!* My experience of publishing dates back to when including a colour pic on an editorial page demanded an appointment with the company accountant. Nowadays there are blogs where colour photographs outstrip the text. Which reminds me of a different way of interpreting the cliché "A picture is worth...": a picture can exclude a thousand words. Frequently, a good thing too.

* Though not here. The only colour images on my outdated clipart disc are only too obviously optical cameras.

DIY in France; science class in Luton

Following my younger daughter's recommendation that I celebrate the sheer painlessness of the DVLA's online tax disc sysem (See, Goodbye to the golden era of vehicle licensing, May 12) I have two suggestions from my older daughter.

Tell them about the set-square, she says. Another Anglo-French moment. Yet again I was engaged in DIY at the house in Loire Atlantique and needed a set-square. A translation exists (l'équerre à dessin) although it looks suspect - sounds more like a T-square. Anyway I didn't have the translation to hand. At the bricolage, I described a set-square's appearance and - rather more demandingly - its function. The assistant listened then said, charmingly,"It sounds like a good idea." But admitted he hadn't got one. There was one in a bubble-pack at the next bricolage.

My older daughter is a teacher's assistant on the science side and her second suggestion relates to my post on Ohm's Law (see Introducing two mega-stars, May 6). Teacher: "Resistance boys, what is resistance?" Class: Blank looks, silence. Teacher: "Imagine I'm outside Burger King and I want to get to Debenhams. At 7 am this would be easy. At 3 pm on a Saturday it would be much harder. Do you see what I mean?"

My daughter adds the coda: So when did resistance have a proportional relationship with time?

NOTE The set-square shown is not the jazzy yellow and chrome one I bought in France. This one belonged to my grandfather, possibly my great-grandfather.

If you open tins here's a must

So why is the Brabantia tin-opener so good? One reason is that significant forces are concentrated at the notched wheel (which drives the opener round the rim of the tin) and the disc blade (which is pressed into the tin end and does the cutting). On cheaper openers the spindles on which these two components rotate wear quickly and both wheel and blade become loose. When the play is so extensive it is almost impossible to squeeze the handles together sufficiently to drive the blade through the end of the tin.

The photo can't show how securely the notched wheel (on the right) is mounted but I can assure you the spindle diameter is twice that of cheaper openers. But the key to the design is the mounting of the blade (which has its own idling notched wheel to grip the other side of the rim of the tin). For one thing the spindle is mounted at an angle. Thus when the driven wheel and blade are squeezed together they operate optimally. Second, even when spindle and blade begin to wear, they are held in position by the curved spring which engages with the free end of the spindle.

I'm afraid it's all a bit wordy. The qualities are easier to understand when you see the Brabantia "in the metal". It only remains for me to add I am not in the pay of Brabantia. I simply like things that work, and this does.

Learn on the couch, not in the car

SATNAV - Part three No, I'm not in thrall to this technology and freely admit it has some way to go. But it's had an undeservedly bad press from people who've tried it for an afternoon, failed to realise its potential and - a particular bête noire - have written delightedly about their inability to penetrate its workings.

One accessory worth acquiring is the cable/transformer that allows you to plug the satnav in to your house supply and play around with it in the comfort of your own living room. You learn far more in this unstressed environment. When you try similar experimentation in the car it always seems too hot and your sweaty finger-tips skitter over the controls.

I think that's enough about satnav. To tell the truth I respond more viscerally to maps but satnav's proof I'm trying to be a child of our times.

TECHNO-ART Other than documentaries which are outside my scope I find TV rather barren of examples in which art fuses with technology. One exception was "Das Boot", the German multi-episode series about life in a WW2 submarine. Here men were surrounded by technology and threatened by it from above. Big batteries were big, too. But I'd appreciate an explanation about that greenish light emanating from small windows - apparently - on the side of the diesel engine cylinders.

Trains - it's not all bad news

"Descanting on his own deformity", Richard III points out he was not shaped for sportive tricks. What I'm not shaped for is mass transport. At 6 ft 2 in. I'm at an immediate disadvantage but the real killer is the distance between my patella and my buttocks. Notably on Japanese Airlines where the relevant seating dimension is a Procrustean 29 in. (vs. 32 in. on the US airline United). A cheap JAL flight to Christchurch, NZ - broken humanely at Tokyo after a mere 11 hr - was paid for in much personal agony.

Buses in Britain are even worse but at least I only use them for short hops. British trains not only cramp my legs but offer minimal space for my feet. Size 10½, since you ask.

Or so I thought for trains have moved on. A perfectly acceptable twin-coach diesel recently took me from Hereford to Newport where a gleaming blue First Great Western monster wafted me painlessly to Paddington.

I commend the seat designer. The accommodation is dense but without menacing my kneecaps or my gluteus maximus. And the seats are cantilevered leaving dance-floor space for my feet. But what I wasn't prepared for were the three-pin sockets, proof that I haven't used a train for yonks.

For years I had noticed people using laptops on trains and assumed they were more confident about their batteries than I have ever been. And then I saw my neighbour's computer was plugged into an unobtrusive 13 A socket. Did he pay for the power? I asked. Oh no.

Just think, I'd be free to compose my blog offline interspersed with innumerable excursions into Solitaire and Columns (a simplified Tetris), both beyond me when I'm driving a car. I may in fact let the train take the strain.

TECHNO-ART Another novel but with a name you'll always remember. "The Gold-bug Variations" by Richard Powers links the technicalities of Bach's music with the application of DNA. The latter field is one I've had difficulty absorbing although I found "The Double Helix" a real page-turner all those years ago. Gold-bug's proposition seemed daring and I read it with interest. But with less understanding. I needed a second opinion and had Amazon send a copy to a friend of mine with a physics background. When we next met he didn't volunteer an opinion and so I was forced to ask him outright. He sighed: "Well, it's very long". I changed the subject.

Why electricity and water don't mix

When you write for the Web you're allowed second thoughts. Typically, I've tweaked the blog explanation on my home page at least half a dozen times.

My piece about Ohm's Law ("Introducing two mega-stars", May 6) deserves a coda. The law itself - current equals voltage divided by resistance - is easily understood. But it's harder to grasp the nature of current and voltage. And, alas, I'm not about to define them. To do so within the confines of this post would be to run up against a barrier in teaching any technical subject where the elements are, and must be, invisible.

Electricity is good and invisible so the instructor uses analogies. "Think of electricity as water flowing through a tap. Voltage is the amount of water flowing, current is the pressure the water is subject to." Are we discussing electricity or hydraulics? And that's as nothing when the instructor must find analogies for coils (inductance) and capacitors (capacitance) which have no useful parallels outside electrical circuits.

It's going to sound like a cop-out but the answer's what you suspected all along. As soon as is humanly possible the instructor junks the analogy approach and starts attaching numerical values to these phenomena. Then he invokes a relationship like Ohm's Law and plugs in the appropriate values. Finally we have a cool clear sentence - as it were - that makes sense. And the language it uses is, of course, mathematics. Not terribly hard maths to begin with. But by the time it's got rather harder the initial maths has been digested.

This sneaky revelation doesn't invalidate my piece about Ohm (and John Donne). His law remains neat and concise, its effects are easily understood and I love it to bits. The next post will be about hammers and nails