82. =Weight.=--I have said before (§ 52) that what we call weight is not a property of matter, but merely the result of a property, the attraction of gravity. This I will now illustrate. If two bodies are falling to the earth, and one of them contains ten times as many particles of matter as the other, ten times as much force of gravity is required, and is actually exerted, to bring it to the ground. This will appear plain to you if you bear in mind that a body does not come to the ground because there is nothing to keep it there, but because it is drawn down by the force of attraction, and then compare this force to any other force, as, for example, that of muscular action. If you draw toward you two weights, one of which is twenty times as heavy as the other, or, in other words, has twenty times the quantity of matter that the other has, you must exert twenty times as much strength on the former as you do on the latter. Just so it is with the force of attraction. The earth attracts or draws toward itself a body having twenty times the quantity of matter that another has with twenty times the amount of force. And the first body will have twenty times the weight of the other, for it will make twenty times the pressure upon any thing that resists the force with which the earth draws it toward itself. Weight, then, is _the amount of the pressure occasioned by the attraction existing between the earth and the body weighed_. If you place a substance in one side of a pair of scales, it goes down because of the attraction between it and the earth. By placing weights in the other side until the scales are balanced, you find how much is needed to counteract the downward pressure caused by the attraction of the substance and the earth for each other; or, in other words, you find out how much it weighs. In doing this you use certain standard weights; that is, certain quantities of matter which have been agreed upon by mankind, and are called by certain names, as pounds, ounces, etc. When a spring is used in weighing, the spring has been tried by these standard weights, and its scale has been marked accordingly.