Mathematics and Physics Glossary

Ultimate ratio (Math.), the limiting value of a ratio, or that toward which a series tends, and which it does not pass.

Ultragaseous, a. (Phys.) Having the properties exhibited by gases under very low pressures (one millionth of an atmosphere or less). Matter under this condition, which has been termed the fourth state of matter, is sometimes called radiant matter.

Ultrared, a. (Phys.) Situated beyond or below the red rays; as, the ultrated rays of the spectrum, which are less refrangible than the red.

Ultraviolet, a. (Phys.) Lying outside the visible spectrum at its violet end; said of rays more refrangible than the extreme violet rays of the spectrum.

Ultrazodiacal, a. (Astron.) Outside the zodiac; being in that part of the heavens that is more than eight degrees from the ecliptic; as, ultrazodiacal planets, that is, those planets which in part of their orbits go beyond the zodiac.

Umbilic, n. (Geom.) An umbilicus. See Umbilicus.

Umbilical point (Geom.), an umbilicus. See Umbilicus.