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: 43 CHAPTER III MEASUREMENT OF WEIGHT 24. Before considering the subject proper of this chapter, we will deal with the meanings of some words in common use, with especial reference to their application in scientific work. First on our list we will put the word "matter". Much learning has been expended on the exact definition of matter, but for our purposes it will be sufficient to consider that " Matter includes everything that we can handle". Thus iron, water, air are all forms of matter, since we can handle them, weigh them, and preserve them for further examination. On the other hand thoughts, heat, and sleep are not composed of matter, since we cannot so treat them. The word "substance" means "kind of matter". Thus iron, water, and air are substances and when we say that iron is a hard substance we mean that all pieces of iron are hard, not simply that one special sample exhibits this quality. When we wish to speak of a special piece of any substance we call it a " body ". Thus we say that a 56 lb. iron weight is a hard body, made of the substance iron. Each body that exists contains a certain quantity of matter. For example, the 56 lb. weight mentioned above contains a certain quantity of iron, and, as long as the weight is protected from the action of substances or forces which may damage the iron in any way, the quantity of iron present in the weight does not alter, as far as we are able to judge in the presentstate of our knowledge. The " quantity of matter " contained in any given body is termed its " mass " and the unalterability of this mass is usually expressed by the phrase " the mass of a body is constant ". 25. We all know that a body, left unsupported in the air, moves rapidly towards the Earth's surface and finally comes to rest on that surface. I...