_Phase._ The aspect of the moon or of a planet depending on the amount of illumination. Position of variation with regard to a real or assumed starting-point. An individual chemical in a mixture. _Phenomenon._ Probably more familiar in the plural: phenomena. Something which is perceived by the senses. An event of scientific interest. _Philology._ The science of language. The philologists have been inclined recently to extend their science, so that it deals with meaning, with folklore or traditional beliefs, and with various other subjects which are more or less closely related to language. _Philosophy._ Literally: the love of wisdom. Former: the sum of knowledge, a complete system of knowledge, sometimes with emphasis upon its use in regulating human conduct. Philosophy is now primarily ethical. Durant insists that the growth of the various sciences makes it all the more necessary to be concerned with philosophy, which directs the proper use of knowledge. Religion, incidentally, is concerned chiefly with the field indicated for philosophy, not with the ground covered by the various sciences. _Phonology._ The study of sounds in speech. _Phosphorus._ A non-metallic element. Symbol: P. _Photics_ or _photology_. The science of light. _Photo-._ In compounds, light or photographic. _Phyllo-._ In compounds, leaf. For instance, Phyllopoda: an order of crustaceans with feet resembling leaves. _Phylo-._ In compounds, tribe, race. As, phylogeny: racial development, the natural history of a type. _Phylum._ One of the largest divisions of animals or plants. _Physics._ The science of matter and energy, not including fields which are considered chemical or biological. _Pistil._ The female organ of a flower, including style, stigma, and ovary. _Planet._ One of the bodies which revolve about the sun, including the earth but not comets or meteors. _Plant._ A living organism which is not an animal. One which does not have sensation or voluntary motion. (This definition must be revised in the light of recent investigations.) Specifically, one of the smaller plants, excluding trees and shrubs. _Platinum._ A metallic element. Symbol: Pt. _Pleistocene._ Of the geological epoch before the Recent, in the Quaternary period of the Cenozoic era. _Pole._ One of the two points in the celestial sphere about which the stars seem to revolve. One of the extremities of the axis of the earth. One of the points on a magnet where magnetic force is manifested. The anode or the cathode of a cell. The extremity of an axis of a spherical or oval cell or organ. _Politics._ The science of government. Popularly, the art of exploiting democratic citizens, as practiced by office-holders and those who control them. _Pollen._ The substance discharged from a flower, fertilizing or male grains. _Pollination._ The carrying of pollen to the pistils. _Polonium._ A substance found in pitchblende, perhaps an element.