The paragraph above may be put into a different form, and made to state that all the physical sciences have been brought up to their present stage, by subjecting the phenomena studied by each science to quantitative investigation. It was by making these quantitative investigations that Newton and the others were able to ascertain the exact facts from which to start in their endeavor to discover the laws of nature; and it was from the laws of nature thus induced that later investigators were able to start on still further expeditions of discovery into the unknown. As the common basis of all quantitative work is mathematics, the common basis of all the physical sciences is mathematics. This makes all the physical sciences interdependent, despite the fact that each is independent of the others. Each one of the physical sciences has contributed its part to building the machine of civilization; the part that each has specially contributed can be clearly specified; and yet, since the machine is the result of the combination of what all have contributed, their contributions are interdependent. This remark applies to the various parts of all machines. The piston of a steam engine, for instance, and the valve that admits steam to the cylinder are entirely separate from each other; but from the mere fact that they both work together, each one must be designed and operated with reference to the other; so that both in their construction and their operation, they are interdependent. Francis Bacon, in the sixteenth century, may be said to have inaugurated the system on which the whole of modern progress has been based, and Newton in the seventeenth century to have taken up Bacon's work and carried it further on. Following Newton, only a few great investigators can be seen in the seventeenth century; but in the eighteenth, began that intense and brilliant movement of investigation, discovery and invention, that has been adding more and more to the machine of civilization--and still is adding more. One of the earliest and most important contributions was an apparatus for measuring time accurately. Who was the inventor is not precisely known. It seems fairly well established, however, that Galileo was the first to call attention to the fact that the vibrations of a pendulum were nearly isochronous, and could be used to measure the lapse of time; and that Galileo's son (as well as Dr. Hooke, Huygens and a London mechanic named Harris, in the early part of the seventeenth century) made clocks based on that principle. It is fairly well established also that Huygens was the first one to make a mathematical investigation of the properties of the pendulum, and to enumerate the laws since utilized for making accurate clocks and watches.