The realities of modern science - 1919 Author:John Mills Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAPTER III WEIGHTS AND MEASURES It has been well said by one of the leading physicists of the 19th century that "when you can measure what you are speaking ... more »about and express it in numbers you know something about it, but when you can not, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the stage of science." In later chapters we shall see how science began, and learn something of the uses of mathematics. To tell "how much," we must have some means for measuring, and a unit. For example, to measure a length we take some length as a unit, that is, call some definite length "one." We may then count how many times this unit goes into the unknown length. The unit we use for this purpose may be a length of any substance, as of string between two knots, for the material of the standard is unimportant provided it is not such as to change its length while we are measuring with it. If a boy wished a measure of how fast he was growing he might record his height each year on some upright. He would not, however, choose a poplar sapling. This illustration makes the use of a variable standardseem very foolish, 1 but such a possibility must always be guarded against, especially when precise measurement is desired. For example, a steel tape line varies in its length, increasing on hot days. In surveying over large areas, as in the case of the U. S. Coast and Geodetic Surveys, extreme precautions are taken in measuring a base line to compensate for such linear expansion. If a tape is used care is also taken that it shall always be under the same tension. For the measurement of length it was natural that the earliest units should be connected with the human body. Thus lengths were measured i...« less