But the story of the steam-engine does not end with Watt. It will be remembered that in the engines of Nero and of Branca the steam did its work by reaction or by impulse. Now soon after the time of Watt, inventors turned their thoughts to the old engines of Nero and Branca and began to experiment with engines that would do their work by a direct impact of steam. After nearly a century of experimenting and after many failures there was at last developed an engine known as the _steam-turbine_. In this engine the steam does its work by impinging or pushing directly upon blades (Fig. 11) which are connected with the shaft which is to be turned, and it does this in much the same manner that we saw the steam do its work in Branca's engine. One of the greatest names connected with the steam turbine is that of Charles Algernon Parsons of England. In 1884 this great inventor patented a steam-turbine which proved to be a commercial success and since that date the steam-turbine has been constantly growing in favor. So great has been its success on land and on sea that there are those who believe that the engine invented by Watt will in time be cast aside and that its place will be taken by an engine which is the most ancient as well as the most modern of steam motors. [Illustration: 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. [Illustration: FIG. 1.--THE KATTA OR DIGGING STICK.]