the wireless appendage to my laptop was attacked by a bendy bus following swiftly on the  kidney punch it gave me, but lo there is a cure for it. Meditating under a No. 53 in repose , if not in Plumstead, should take care of the other ailment.

Allen Brown (Letters, September) asks whether there is any explanation as to why electric light bulbs sometimes ‘sing’ just before they fail. If a lamp filament fails during use and the break is not sufficient to interrupt the current, an arc will form across the break. Arcs formed in this way can be surprisingly long if the ends of the filament move. The singing is the sound of the this discharge, possibly acoustically modified by the thin glass envelope. Therefore filament lamps start to sing when they fail and not before. On a safety note, as this discharge is a UV source it is not advisable to look at a ‘singing lamp’ in view of the chance of ‘arc eye’, but to switch it off. If the singing was due to arcing across a break, the lamp will of course not light again.

I first met the ‘singing light bulb’ effect as a very junior technical assistant in a lampworks in the mid-1930s. Part of my job was to inspect the life-test racks twice daily, perform the BSI 161-1936 specified interruptions in supply, and record failures. Out of several hundred lamps on test, it was not uncommon to find one ‘singing’. The explanation is, of course, that the tungsten coil, having suffered long, has now parted at its weakest point and is now arcing using the remains of the tungsten coil as ballast. Left undisturbed it may run for some hours, depending largely upon the pressure and purity of the gas filling.