Part 15

Homology. That relation between parts which results from their development from corresponding embryonic parts, either in different animals or in the same individual.

Hormone. A stimulating substance carried from one organ to another.

Horse-power. The unit of power in the English system. It is equal to 550 foot pounds per second.

Humidity. Moisture.

Hurricane. A wind of stormy violence.

Hybrid. The offspring of two plants or animals of different sorts.

Hydrate. A compound containing combined water.

Hydraulics. The science dealing with liquids in motion.

Hydrocarbon. A compound of carbon and hydrogen.

Hydrogen. A gaseous element. Symbol: H.

Hydrolysis. The decomposition of water in such a reaction as includes the formation of new compounds with the hydrogen and the oxygen of the water.

Hydrometer. An instrument used to determine the specific gravity of a liquid.

Hydrostatics. The science which deals with the pressure of liquids.

Hydrous. Containing water, whether in combination or in a mixture.

Hydrozoan. A member of a class (Hydrozoa) of coelenterate animals, chiefly marine, including jellyfish.

Hygiene. The science of sanitation, preventive medicine. In the United States, textbooks of hygiene are chiefly concerned with proving that alcohol and tobacco are injurious. Here is an example of “science” created by legislative fiat.

Hygrometry. The measuring of atmospheric moisture.

Hypothesis. A supposition used as a basis for reasoning, a provisional explanation. If it appears to be unconfirmed by the facts, it is rejected. Otherwise it becomes a theory, then a law.

Igneous. Formed by great heat, as rocks.

Indehiscent. Not bursting open at maturity.

Indium. A metallic element. Symbol: In.

Indo-European or Indo-Germanic. Pertaining to a great family of languages including most of those spoken in Europe and by the white men in America as well as some used in India and other parts of Asia.

Inductance. The electrification of a conductor placed near a circuit or charged body, resulting from the proximity.

Inert. Not easily made to react.

Inertia. The property of matter by which it tends to remain at rest if it is at rest, or, if it is in motion, to remain in motion in a straight line. Our notion of inertia may possibly be changed by Einstein’s theory.

Inflorescence. Flowering, the arrangement of flowers on a plant.

Infra-. In compounds, below.

Infusoria. A class of protozoa which possess hairlike outgrowths.