How far the composition of words, in such cases, may be practised in the English language, and the general question, what are the best rules and artifices {264} in such cases, I shall afterwards consider. In the mean time, I may observe that this list of invented technical terms might easily be much enlarged. Thus in harmonics we have the various intervals, as a _Fourth_, a _Fifth_, an _Octave_, (_Diatessaron_, _Diapente_, _Diapason_,) a _Comma_, which is the difference of a _Major_ and _Minor Tone_; we have the various _Moods_ or _Keys_, and the notes of various lengths, as _Minims_, _Breves_, _Semibreves_, _Quavers_. In chemistry, _Gas_ was at first a technical term invented by Van Helmont, though it has now been almost adopted into common language. I omit many words which will perhaps suggest themselves to the reader, because they belong rather to the next class, which I now proceed to notice. III. The third class of technical terms consists of such as are constructed by men of science, and involve some theoretical idea in the meaning which their derivation implies. They do not merely describe, like the class last spoken of, but describe with reference to some doctrine or hypothesis which is accepted as a portion of science. Thus _latitude_ and _longitude_, according to their origin, signify breadth and length; they are used, however, to denote measures of the distance of a place on the earth's surface from the equator, and from the first meridian, of which distances, one cannot be called _length_ more properly than the other. But this appropriation of these words may be explained by recollecting that the earth, as known to the ancient geographers, was much further extended from east to west than from north to south. The _Precession_ of the equinoxes is a term which implies that the stars are fixed, while the point which is the origin of the measure of celestial longitude moves backward. The _Right Ascension_ of a star is a measure of its position corresponding to terrestrial longitude; this quantity is identical with the angular ascent of the equinoctial point, when the star is in the horizon in a _right_ sphere; that is, a sphere which supposes the spectator to be at the equator. The _Oblique Ascension_ (a term now little used), is derived in like manner from an oblique sphere. The motion of a planet is _direct_ or _retrograde_, _in_ {265} _consequentia_ (_signa_), or _in antecedentia_, in reference to a certain assumed standard direction for celestial motions, namely, the direction opposite to that of the sun's daily motion, and agreeing with his annual motion among the stars; or with what is much more evident, the moon's monthly motion. The _equation of time_ is the quantity which must be added to or subtracted from the time marked by the sun, in order to reduce it to a theoretical condition of equable progress. In like manner the _equation of the center_ of the sun or