ELASTIC. That power which a body has of returning to the form from which it has been distorted. Thus, the branch of a tree, the blade of a sword, :Ice. are said to be elastic, because, if they are bent to a certain degree, and then let go, they will of themselves return to their original form. Hence elastic bodies are such as admit of having their form altered by the application of a force or pressure, on the removal of which they will recover their original form or figure. In this respect, all bodies which come within our knowledge, are comprehended under one of these three dis tinctions. If two bbdies, when pressed to gether, suffer an alteration in their form, and if, afterwards, on removing that pressure, they recover their original figures, they are called elastic. if; When pressed, their forms are net in the least altered, they are called hard. And iC when being pressed as above, they al ter their forms, and retain the same after the premise is discontinued, they are called soft And both these last kinds of bodies are termed non ellssic. We know, however, of no bodies
that are perfectly hard, soli, or elastic, but all partake of these qualities in a greater or less degree. Water was a long time supposed to he incompressible, and perfectly non-elastic; but experience shows that this supposition was erroneous ; and air, which is the most elastic fluid we know of, is now known not to pos sess that property in a perfect degree. Van one hypotheses have been advanced by philo sophers to accsuunt for this important proper ty, some attributing it to one cause, and some to another; - it is, however, now more general ly supposed to arise from the presence of ca loric, and the attractive and repulsive powers that have place between the minute particles which constitute a body, whether solid or fluid.