Light economized by rightly-shaped glass. Heat saved by well- designed conveyors and radiators. Why rough glass may be better than smooth. Light is directed in useful paths by prisms. The magic of total reflection is turned to account. Holophane Globes. Prisms in binocular glasses. Lens grinding. Radiation of heat promoted or prevented at will 72 VIII. FORM CONTINUED. TOOLS AND IMPLEMENTS Tools and implements shaped for efficiency. Edge tools old and new. Cutting a ring is easier than cutting away a whole circle. Lathes, planers, shapers, and milling machines far out-speed the hand. Abrasive wheels and presses supersede old methods. Use creates beauty. Convenience in use. Ingenuity spurred by poverty in resources 89 IX. FORM CONTINUED. ABORIGINAL ART Form in aboriginal art, as affected by materials. Old forms persist in new materials. Nature’s gifts first used as given, then modified and copied. Rigid materials mean stiff patterns. New materials have not yet had their full effect on modern design 108 X. SIZE Heavenly bodies large and small. The earth as sculptured a little at a time. The farmer as a divider. Dust and its dangers. Models may mislead. Big structures economical. Smallness of atoms. Advantages thereof. Dust repelled by light 120 XI. PROPERTIES Food nourishes. Weapons and tools are strong and lasting. Clothing adorns and protects. Shelter must be durable. Properties modified by art. High utility of the bamboo. Basketry finds much to use. Aluminium, how produced and used. Qualities long unwelcome or worthless are now gainful. Properties created at need 135 XII. PROPERTIES CONTINUED Producing more and better light from both gas and electricity. The Drummond light. The Welsbach mantle. Many rivals of carbon filaments and pencils. Flaming arcs. Tubes of mercury vapor 154 XIII. PROPERTIES CONTINUED Steel: its new varieties are virtually new metals, strong, tough, and heat resisting in degrees priceless to the arts. Minute admixtures in other alloys are most potent 163 XIV. PROPERTIES CONTINUED Glass of new and most useful qualities. Metals plastic under pressure. Non-conductors of heat. Norwegian cooking box. Aladdin oven. Matter seems to remember. Feeble influences become strong in time 180 XV. PROPERTIES CONTINUED. RADIO-ACTIVITY