ulls of animals, and
cup-shaped stones filled with fat or fish oils which burned on a wick of
cloth or the pith of rushes. The Tibetans burn butter, the Eskimos
whale- or seal-oil, the Arabians palm- or olive-oil. For outdoor
lighting, torches carried in the hand were used till gas came into
general use about 1792.

CONDUCTION

Give to four boys strips of copper, aluminium, wood, and glass,
respectively. They hold these by one end and heat the other end till one
or more are forced to drop the piece on account of the heat. The boys
with the metals will soon find them hot throughout, but the other two
will be able to hold on indefinitely. The teacher gives the terms "good
conductor" and "poor conductor".

PROBLEMS

1. Are metals generally good conductors? Try with strips of zinc, lead,
iron, a silver spoon.

2. Are all good conductors equally good? Devise a means of ascertaining.
See _Science of Common Life_, Chapter VI; also _The Ontario High School
Physics_, page 274.

3. Is water a good conductor?

Lists of good and poor conductors may then be made, the teacher adding
to the list. Good: metals; poor: wood, horn, bone, cloth, leather, air,
water, hair, asbestos, ashes, rock, earth.

PROBLEMS

1. If the interior of the earth is very hot, why do we not feel it?

2. How can the cold snow keep the earth warm?

3. Why does your hand freeze to metals but not to wood?

4. Let the children try to find other instances: wools or furs for
clothing, fur coats on northern animals, feathers on birds, down quilts,
tea cosies, sawdust for packing ice, double windows, wooden handles for
hot irons, asbestos coating for steam pipes.

THE MINERS' SAFETY-LAMP: This is a most important application of
conduction. Get from the tinsmith a piece of brass gauze six inches
square. Raise the wick of the spirit-lamp causing it to give a high
flame and bring the gauze down upon the flame till it touches the wick.
Note that the flame does not rise above the gauze. Hold a piece of paper
above the gauze near the flame and note that it does not take fire. Note
also that the gauze soon becomes hot. The brass wires conduct the heat
of the flame rapidly away so that there is not heat enough above the
gauze to cause combustion. Now roll the gauze into a hollow cylinder,
pin the edges together, insert a cork at each end, and have a short
candle fastened to the lower one. Try to light the candle with the lamp
through the gauze. It is not easi