In a like way, all the laws that investigators have put into concrete and usable form, have been used by other investigators as bases for further investigations, and by inventors as bases for future inventions. Even the inventor of the fist-hammer had to know something about the material which he employed; he had to know that it was hard and heavy, for instance, and that it could be hammered so as to have a point and a sharp edge. He had to know also something about the flesh of a man: he had to know that if his flesh was struck with a sharp hard instrument, it would be bruised, and the man injured, and maybe killed. Similarly, the inventor of the gun, and the inventor of printing, and the inventors of steam engines, had to know a good deal about the materials which they employed, and about the uses to which their appliances could be put. Naturally, they had to know much more than did the inventor of the fist-hammer. But the inventor of today has to know still more, because there is still more to know. An inventor of the present day who knew no more about physical science than Galileo did would not be able to go far. A like remark may be made about any man in any vocation, as compared with his predecessor in Galileo's time. The machine of civilization is so vast and so complex, that the amount of knowledge which anyone of us needs in mere daily life is almost incredible. Let anyone try to enumerate all the facts he knows! The attempt will convince him quickly. It may be pointed out here that, while modern civilization differs from ancient civilization in many ways, it differs more in complexity than in any other one way. Some of the factors of ancient civilization were as good as those of today; such things, for instance as temples and pyramids and stationary objects in general. But the ancients did not understand motion clearly, especially irregular motion; and they had no fast vehicles of any kind. Their knowledge of statics must have been fairly complete, or they could not have built their temples and pyramids; but their records show little understanding of dynamics. Now the basis of dynamics is mathematics. Dynamics is the result of the application of mathematics to the observed effects of force on bodies, in producing motion. Dynamics is a branch of the science of mechanics, and a most difficult branch. It is built on the observations, calculations and conclusions of Newton and a host of experimenters and mathematicians of lesser mentality, and it could not have come into being without them.