53. =Nature of Attraction.=--If you attempt to break a very tenacious solid substance, why do you not succeed? It is because the particles are so strongly fastened together. But how? By some kind of cement or glue, or by some mechanical contrivances as nails or hooks? No. They are fastened together by some unseen force. We know nothing of the nature of this force. We know only that it exists, and we call it attraction. The name is a proper one, for it simply expresses the fact that one particle attracts or draws another particle toward itself. 54. =Newton's Idea of Attraction.=--It was stated in § 20 that the particles of matter, even in the densest substances, are not in actual contact, but have spaces around them. Now it was supposed by Newton that there is some kind of ethereal substance pervading all these spaces, which causes this attraction between the particles. He supposed also that this ether was every where in space, causing attraction between masses of matter. But all this is mere supposition, and we know not whether there is this sort of ethereal glue keeping the universe together, or whether it is some property in the particles themselves that makes them thus attract each other. But the fact of the attraction we know, and we can observe the phenomena which it produces, and discover the laws or rules by which this force is regulated in its action. 55. =Attraction in Solids.=--Attraction is stronger in some solids than in others. The mason with his trowel easily divides a brick; but he can not do this with a piece of granite, for its particles have a greater attraction for each other than those of the brick. So a rap which would break a glass dish would not injure a copper one of the same thickness. A weight that would hang securely from an iron wire would break a lead wire of the same size; that is, it would tear the particles apart, because they are not strongly attracted to each other. Attraction has different modes of action in different solids. It therefore fastens their particles together in different ways, and thus produces all the various qualities, already noticed, which are so useful to us--tenacity, hardness, softness, ductility, flexibility, etc. 56. =Attraction in Liquids.=--In a liquid the attraction between the particles is very feeble compared with that in solids. The attraction of the particles of steel is in strength about three million times that of the particles of water. We make the estimate in this way: We find that a steel wire will sustain a weight equal to 39,000 feet of the wire. But a drop of water hanging to the end of a stick can not be more than one-sixth of an inch in length; that is, water will hold together by the attraction of its particles only to this extent, which is a little less than the three millionth part of the length of steel wire which could hang without breaking.