FIG. 11.—SHAFT OF A LARGE MARINE TURBINE.
Within the cylinder are thousands of blades upon which the steam acts directly in the turning of the shaft. In the largest turbines there are as many as 50,000 blades.
[THE PLOW]
You have now learned the history of those inventions which enabled man to gain a mastery over fire and to use it for his comfort and convenience. We shall next learn the history of an invention which gave man the mastery of the soil and enabled him to take from the earth priceless treasures of fruit and grain. This invention was the plow.
In his earliest state man had no use for the plow because he did not look to the soil as a place from which he was to get his food. The first men were hunters and they relied upon the chase for their food. They roamed from place to place in pursuit of their prey—the birds and beasts of the forest and the fishes of the stream. They did not remain long enough in one spot to sow seed and to reap the harvest. Still in their wanderings they found wheat and barley growing wild and they ate of the seeds of these plants and learned that the little grains were good for food. They learned, too, that if the seeds were planted in a soil that was well stirred the plants would grow better than they would if the seeds were planted in hard ground. So by the time men had grown tired of wandering about and were ready to settle down and live in one spot they had learned two important facts: they knew they could add to their food supply by tilling the soil, and they knew that they could grow better crops if they would stir the soil before planting the seed.
FIG. 1.—THE KATTA OR DIGGING STICK.
For the stirring of the soil the primitive farmer doubtless first used a sharpened stick such as wandering tribes carry for the purpose of digging up eatable roots, knocking fruits down from trees, and breaking the heads of enemies. Such a stick known as the Katta (Fig. 1) is carried by certain tribes in Australia, and we are told by travelers that the Kurubars of Southern India use a sharp stick when digging up the ground. The digging stick is used by savages in many parts of the world and we may regard it as the oldest of implements used for tilling the soil.