[Illustration]
On a good-sized cork or bung place a small lighted taper, and then set
it afloat in a pail of water. Invert a large drinking-glass over the
light, and push it carefully down into the water. The glass being full
of air, prevents the water entering it. The candle will burn under
water, and come up again to the surface still alight. The largest
drinking-glass holds but half a pint, so that your diving light soon
goes out for the want of air. A burning candle consumes as much air as a
man, and he requires nearly a gallon of air every minute, so that,
according to the size of the glass over the flame, you can calculate how
many seconds it will remain alight, a large flame requiring more air
than a small one. A quart bell-glass is very useful. A substitute is
easily made from a green glass pickle bottle, with the bottom cut off.