in Physics, the act of changing the circumstances and manner of a thing, its general nature and appearance remaining the same; or it is an accidental and partial change in a body, without proceeding so far as to make the subject quite unknown, or to take a new denomination thereupon; or it may be defined, the acquisition or loss of such qualities as are not essential to the form of the body. Thus, a piece of iron which before was cold is said to be altered when it is made hot, since it may still be perceived to be iron, is called by that name, and has all the properties thereof. By this, alteration is distinguished from generation and corruption, those terms expressing an acquisition or loss of the essential qualities of a thing. The modern philosophers, after the ancient chemists and corpuscularians, hold all alteration to be effected by means of local motion. According to them, it always consists either in the emission, accession, union, separation, or transposition, of the component particles.