ABSTRACT
Terms of a scientific sort are accordingly meaningful in reference to a system of concepts which have been formed to explain the nature of the physical universe. And since changes of meaning come with changes of systems and philosophies, the ideal scientific term would supply an exact reference to the particular scheme of thought and ultimately the philosophy which authorized its use in a particular context. Since scientific knowledge is carried from one generation to another largely by means of written records, the terminology employed should be as nearly fixed as possible. Yet, as new theories are constructed and others modified or done away with, and as knowledge is increased, many of the terms that survive suffer important changes of meaning. The changes which transform fire into water, then into earth, form the up-road. The changes which inversely transform earth into water, then into fire, are called the down-road.
