I SO 



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J UK 



This order embraces the genus 

 Oniscus. 



ISO'SCELES. (iffoffKeXfo, Gr.) That 

 which hath only two sides equal. 



I'SOPYEE. A mineral of a greyish 

 or black colour. Occurs massive. 

 Found in Cornwall, imbedded in 

 granite. 



ISO'THEKAL. (from foos and Oepos, 

 summer, Gr.) Of the same summer 

 temperature : lines drawn through 

 places having the same summer 

 temperature are denominated iso~ 

 tJieral lines. 



ISOTHE'EMAL. (from "ao? and O^p^, 

 Gr. ) Possessing equal temperature. 

 Lines drawn upon a map through 

 a series of places having the same 

 annual mean temperature are termed 

 isothermal lines, or lines of equal 

 temperature. Sir C. Lyell observes, 

 "it is now well ascertained that 

 zones of equal warmth, both in the 

 atmosphere and in the waters of 

 the ocean, are neither parallel to 

 the equator nor to each other. It 

 is also discovered that the same 

 mean annual temperature may exist 

 in two places which enjoy very 

 different climates, for the seasons 

 may be nearly equalized or vio- 

 lently contrasted. Thus the lines 

 of equal winter temperature do not 

 coincide with the lines of equal 

 annual heat, or isothermal lines. If 

 lines be drawn round the globe 

 through all those places which have 

 the same winter temperature, they 

 are found to deviate from the ter- 

 restrial parallels much farther than 

 the lines of equal mean annual heat. 

 The lines, for instance, of equal 

 winter in Europe, are often curved 

 so as to reach parallels of latitude 

 9 or 10 distant from each other, 

 whereas the isothermal lines only 

 differ from 4 to 5." 



ISOTHE'EMAL ZONES. As the isothermal 

 lines are as numerous as the places, 

 and as diversified as numerous, 

 geographers have grouped them 

 into bands or zones. Humboldt 



has divided the northern hemi- 

 sphere into six isothermal zones or 

 bands. 



FSOTOME. Isotomes are those bodies 

 which have the same crystalline 

 form, and similar formula, and 

 equal atomic volumes. 



ISTIU'EUS. A genus of that family of 

 saurians called iguanida, and thus 

 named by Cuvier. The distin- 

 guishing character of the genus 

 Istiurus is an elevated and trench- 

 ant crest, extending along a portion 

 of the tail, and supported by spi- 

 nous apophyses of the vertebra. 



ITJ'LUS. ) ,,, , n x 



JU'LTTS. jO^Gr-) 



1. In botany, a catkin; a species 

 of inflorescence consisting of chaffy 

 scales arranged along a stalk ; they 

 are worm-like tufts, which at the 

 beginning of the year grow out, 

 and hang pendular down from the 

 hazel, walnut, filberd, &c. 



2. In zoology, a genus of insects of 

 the order Aptera. The feet are 

 very numerous, being on each side 

 twice as many as the segments of 

 the body ; the antennas are moni- 

 liform; there are two articulated 

 palpi ; and the body is of a semi- 

 cylindrical form. There are many 

 species. 



I'VOBY. (elur, Lat. ivoire, Pr. avdrio, 

 It.) A hard, solid, and firm sub- 

 stance, of a white colour, and ca- 

 pable of a very good polish. It is 

 the tusk of the elephant. The 

 ivory from Ceylon is more valuable 

 than any other, from its not be- 

 coming yellow in the wearing, as 

 nearly all other ivory does. 



JT/RA LIMESTONE. fcalcaire de Jura, 

 Jura kalk.J The name given by 

 some continental geologists to that 

 group of rocks comprised in the 

 oolite. The Jura limestone group 

 is composed of limestones of various 

 qualities, clays, sands, and sand- 

 stone, and contains the same fossils 

 as those found in the oolitic group 

 of England. In the range of the 



