ULM 



ULT 



to the ammonites, having the siphunicle 

 near the dorsal margin. 



TU'TENAG. The commercial name for 

 the zinc or spelter of China, an alloy used 

 in the manufacture of the gong ; also the 

 name of a white metallic compound, 

 called Chinese copper. Impure oxide of 

 zinc is called tutty. 



TWILIGHT. A phenomenon depend- 

 ing on reflection of the rays of light pass- 

 ing through tlie atmosphere. Before the 

 sun becomes visible above the horizon, 

 the rays of light illuminate the atmo- 

 sphere, vi^hich to some extent reflects and 

 scatters them in all directions, and the 

 result is a faint light which precedes the 

 rising of the sun and follows its setting, 

 and which we call twilight. Twilight 

 begins and terminates when the sun is 

 about 18° below the horizon ; its dura- 

 tion varies with the latitude; in some 

 northern latitudes it may endure all 

 night. The luminous lines occasionally 

 seen in the air, in a sky full of partially 

 broken clouds, which the vulgar term 

 " the sun drawing water," are similarly 

 caused. 



TYCHONIC SYSTEM. A system of 

 Astronomy, so named from Tycho Brahe, 

 a noble Dane, who was born a.d. 1546, 

 and who partly restored the system of 



Ptolemy concerning the earth remaining at 

 rest, whilst the other heavenly bodies moved 

 round it. He taught, however, that the 

 moon performed a monthly revolution 

 round the earth; that the sun was the 

 centre of the orbits of Mercury, Venus, 

 Mars, Jupiter, and Saturn, which revolve 

 round him in their respective periods, as 

 he revolves round the earth in a solar 

 year; and accordingly, that these five 

 planets, together with the sun, are car- 

 ried round the earth in twenty-four hours. 

 TYPE METAL. An alloy of lead and 

 antimony, used in casting printer's types. 

 TYPHLOPHTHA'LMES (ru^Xor, 

 blind, b(p0a\iJ.6s, the eye). A family of 

 Scincoidans, comprising those Saurians 

 which are completely blind, or whose 

 eyes are so small that they seem scarcely 

 to exist, except in a rudimentary state, 

 and entirely covered with skin, as in the 

 genera dibamus and typhline. 



TYPHOON {TV(pwv, a whirlwind). A 

 hot wind which occasionally blows with 

 great violence in Africa, Syria, Arabia, 

 and Persia. It is known in Egypt by the 

 name of sirocco, in Arabia as the simoon, 

 and on the coast of Guinea as the har- 

 mattan. The term is frequently applied 

 to a tropical storm. 



U 



ULLMANNITE. Phosphate of man- 

 ganese and iron, occurring massive at 

 Limoges in France. 



ULMA'CEiE {ulmus, the elm). The 

 Elm tribe of Dicotyledonous plants. 

 Trees and shrubs with leaves alternate ; 

 flowers apetalous ; ovarium superior ; 

 fruit 1 or 2-celled, indehiscent ; seeds 

 pendulous, 



ULMIC ACID, or ULMIN {ulmus, the 

 elm). The name given by Dr. Thomson 

 to a brown substance derived from a se- 

 cretion of the elm and some other trees, 

 consistinjg of mucilaginous matter com- 

 bined with potash. Berzelius changed 

 the name for that of geic acid {-yri, earth), 

 because, on treating soils with alkalis, 

 a considerable quantity of a similar com- 

 pound is obtained. The peculiar pro- 

 perties of manures, soils, and what is 

 called moss-water, are due to the pre- 

 sence of this substance. 



Sacchulmic acid. This substance, apd 

 sacchulmine, are formed by boiling cane 

 351 



sugar for a very long time in dilute sul- 

 phuric, hydrochloric, or nitric acid. They 

 were supposed to be identical with ulmic 

 acid and ulmin, but Liebig considered 

 them to be of a different nature, and gave 

 them their present names. 



ULTIMATE ANALYSIS. In che- 

 mistry, the resolution of substances into 

 their absolute elements, as opposed to 

 proximate analysis, by which they are 

 merely resolved into secondary com- 

 pounds. These terms are generally used 

 in reference to organic bodies. Gum, 

 starch, &c., are proximate principles ; 

 carbon, hydrogen, and oxygen, ultimate 

 principles. 



ULTIMATE RATIO. The ratio of 

 evanescent quantities. If two variable 

 quantities be supposed constantly to ap- 

 proach each other in value, so that their 

 ratio or quotient continually approaches 

 to unity, and at last differs from unity by 

 less than any assignable quantity, the 

 ultimate ratio of these two quantities is 



