MAGNETIC IRON FILING SAND TIMER
Time Marches On
No, it doesn't; it runs out. See for yourself with this hourglass full of iron filings. The steel base has a magnet, so time flies when the glass is on it, and the filings make pretty stalagmites. Stick a magnet on the neck, however, and you can stop time altogether. Glass is 5-1/2" tall on the base and filings run out in about 40 seconds (three trips make a two-minute egg) with the magnet, somewhat longer without it.
Beauty Of A Stirling Engine