ly done.

The miner carries a lamp made like this, so that if he should be in the
presence of the explosive gas, "fire damp", it would not explode because
of the wire gauze shield.

CONVECTION

Water is not a conductor, how then is it heated?

Drop a few pieces of solid colouring matter, (analine blue, blueing, or
potassium permanganate) into a beaker of cold water. Place the beaker
over a heater and observe the coloured portion rise.

Wet sawdust will make a good substitute for the colouring matter. A
sealing jar or even a tin cup will do instead of the beaker. The stove
or a dish of hot water will take the place of the lamp.

PROBLEMS

1. Using a thermometer, see whether the water at the bottom is warmer
than that at the top while the beaker is being heated.

2. Heat some oil and pour it over the surface of some cold water. Lower
a thermometer into this. Does the water at the bottom soon become warm?

3. If your kitchen is provided with a hot-water tank, find out what part
of the tank first becomes warm after the fire is lighted.

4. In bathing, where do you find the coldest water of a pond or still
river? See _Science of Common Life_, Chapter VI; also _The Ontario High
School Physics_, page 280.

CONVECTION IN GASES

A good apparatus may be made by cutting two holes one inch in diameter
in one side of a chalk box, replace the lid with a piece of glass, place
a lamp chimney over each hole and a lighted candle under one of the
chimneys. Hold a piece of smoking touch-paper at each chimney in turn
and note direction of air current.

APPLICATIONS

1. Winds are caused by the rising of air over heated areas, allowing
cooler currents to take its place. (Geography)

2. Rooms are ventilated by heating some of the air more than the rest,
thus producing a current. (Hygiene) Winds are nature's means of
ventilating the earth.

RADIATION OF HEAT

This should be taken up as an introduction to dew, frost, winds,
climate, etc.

1. Make an iron ball hot (the end of a poker will answer). Hold the hand
a few inches below the iron. Does the heat reach the hand by convection?
By conduction? By means of suitable questions, lead the pupil to see
that it is not by convection, for the hand is below the hot object while
heated air rises; it is not by conduction, for air is one of the very
poorest conductors; moreover, the heat is felt instantly from the poker,
but it takes an appreciable time for it to come by conduction