Bits of useful information

Long ago we used to set fire to a bit of paper by focusing the sun on it through a lens. Dramatic results. Some "class comedians" would even focus the sun onto someone's flesh, to see them jump when the heat struck home and they started to burn.

I remember this whenever I have to put down my reading glasses in a patch of sunlight, and I make sure that they are not the way round that the light would focus onto anything a few inches away (for the same reason that you should never, ever, look directly at the sun through a lens).

When I worked I had an a swipe card to get into work that kept invalidating my credit cards.

It was only after several weeks that I was told I should not keep the work swipe card in my purse with credit cards.