It is remarkable that all this time Guericke had not heard of the wonderful experiments made in Italy by Torricelli, the pupil of Galileo. Had he done so, he might have been led to try to obtain a good vacuum by means of mercury, as is done nowadays. But in some respects his apparatus was greatly superior to that used by the Italians. In order to find whether animals could breathe in rarefied air, some of the Italians brought birds and other small animals into the vacuum at the top of the column of mercury. It was found, of course, that the animals could not live, partly because air was necessary for breathing, and partly because their whole structure and constitution was disturbed by the pressure of the air within them, which was no longer counterbalanced by the pressure outside. Such experiments as these, together with others on combustion, could be performed much better with the air-pump as constructed by Guericke; although it must be borne in mind that such experiments on animals are not now necessary, since we know that animals cannot survive after they are deprived of air. The effect of the invention of the air-pump was very great. Men realised for the first time that they lived at the bottom of an ocean of air; and that if all air were removed, the world would be quite different. It would be a world in which neither animals nor human beings could live. The air-pump in the course of the next century led to two other great inventions, the steam-engine and the balloon. CHAPTER VIII THE INVENTOR OF THE STEAM-ENGINE IT has long been supposed that the steam-engine was invented by an Englishman of the name of James Watt. But the real inventor of the steam-engine was Denis Papin, a French doctor, who invented the engine while in Germany, and described it in a book which he published in England, where he lived for many years. He made friends with Huygens in Paris, and assisted him in carrying out his experiments on the air-pump. [Illustration: Fig. 40.--Papin’s improved Air-Pump.] Huygens was very busy with a great variety of inventions, and was glad to have this young assistant, who would carry out experiments for which he himself had no time. Papin made a number of improvements in the air-pump. One of these was a cock, constructed on the principle of a gas cock or water tap, but having two channels through it. Another great improvement which he made in the air-pump was that he put the objects under a glass shade instead of in a bottle. The shade was placed upon a flat plate, and its edge was well greased, so that no air could enter from below. [Illustration: Fig. 41.--One of Papin’s Experiments. A bladder containing very little air swells up when a vacuum is produced in the bell-jar, owing to the expansion of the air contained in it.]