and this…’ he picked up the flat plastic disc ‘… were in the same area.’ He turned the plastic disc over to reveal a clock face on the other side.‘There should also be at least one other piece of wire somewhere, and some of the clock case and a battery or two, but we haven’t found those yet. This was not actually an alarm clock, I don’t think. We’ve found no sign of an alarm mechanism.’
‘No, it won’t have been an alarm clock,’ I said.
The superintendent had been growing restive during Smith’s account and could contain himself no longer.
‘Will you please explain your familiarity with this device,’ he said formidably.‘Did the gardener use this sort of thing for blowing up the tree trunk?’
‘No, I don’t think so. This device wasn’t meant for setting off bombs. It was a toy.’
‘What sort of toy?’
‘Well… it was for switching things on. Torch bulbs, mostly. Like the lights we had on a station in a train set. A buzzer, sometimes. It was incredibly simple.’
‘Explain,’ Yale commanded.
I glanced at Smith. He was nodding resignedly.
‘You get an old or cheap dock,’ I said.‘We had wind-up clocks, not a battery clock. You fix a length of wire to one of the hands, like this, so that a bare bit of wire sticks out and makes the hand much longer.’
‘The hands are still on the clock, I take it?’
‘Oh yes. Though sometimes we’d pull the minute hand off and just use the hour hand, because it’s stronger, even though it’s shorter. All you need is for the bare wire to reach out beyond the edge of the clock face. We used glue to stick the wire to the hand. Then you have a long bit of wire coming out from the centre of the front of the clock, and you fasten the free end of that to a battery. One of those nine-volt batteries with things like press-studs at the end.’ Smith was still nodding. Yale looked very much as if I shouldn’t know such things.
‘We made quite a lot of other gadgets,’ I said, hearing the defensiveness in my voice.‘Buzzers for morse codes. Rudimentary telephones. Not just time-switches. I made a lock once which could only be operated with a straight piece of wire.’ And it still worked fine, although I wasn’t going to show him.
Yale sighed.‘So in this case, we’ve got the wire fixed to the clock’s hand at one end and to a battery at the other, right? Go on from there.’
‘You need two more lengths of wire. One goes from the battery to whatever you want to activate. In our case, it was usually a torch bulb screwed into a metal holder. We fastened a bare end of wire to the metal holder. Then the third wire went back from the metal holder to the clock. We fixed this wire with glue to the clock case itself, not to the hands, in such a way that the bare end of wire was pointing out forwards, towards you if you were facing the clock like this.’ I demonstrated with the clock face.‘We usually stuck it on over the number twelve, at the top, but you could fix it anywhere you liked. Then you wind up the clock and set the hand with the wire where you want it, and just wait. The wired hand travels round towards the jutting out wire and eventually hits against it at right angles. The circuit is thus complete from the clock wires to the battery to the light and back to the clock, so the light goes on. The clock hand keeps on trying to go round and the jutting wire keeps stopping it, so the light stays on. Well…’ I finished lamely,‘that’s what happened when we made them.’
‘Them?’ Yale said with apprehension.
‘They were easy to make. They were interesting. I don’t know how many we had, but quite a few.’
‘My God.’
‘There might be one still in the playroom,’ I said.‘The old train sets are there.’
Yale looked at me balefully.‘How many of your family saw these devices?’ he asked.
‘Everyone.’
‘Who made them?’
‘I did, Gervase did, and Ferdinand. Thomas did. I don’t remember who else.’
‘But your whole family knows how to make a simple time-switch?’
‘Yes, I should think so.’
‘And why,’ he said,‘haven’t you mentioned this before?’
I sighed and twisted the wired clock hand round in my fingers.‘Because,’ I said,‘for starters I didn’t think of it until after I’d left here the other day. After we’d been digging out the black powder