HYPSOMETRY. 411 HYRAX. ing (see Leveling) only in the greater accuracy of the methods and instruments used. For measuring heiglits by barometric observa; lions the form of barometer known as the aneroid barometer is usually used. Mercury barometers may of course be used, but usuallj' they are not, owing to the greater dilllculty in transporting them and of keeping them in projjcr working <irder. The adaptability of the barometer as an instrument for measuring heights depends upon the facts that the mercury column falls as the atmospheric pressure decreases, and that the atmospheric pressure decreases gradually as we ascend above the sea-level. As a rovigh average it may be assumed that the barometer falls 1-10 inches for about 100 feet rise. To measure the height .IX, therefore, barometer readings are taken simultaneously at .s and at x, and from them the difference in height of s and x may be found by the formula, d = GOOD (log. H-log. fc) (l + l±±=.^^j in which d equals the diflerence in height; H and h are the two readings, and T and t are the tcm- jjerature of the two stations in degrees Fahren- heit. In the most accurate barometric work va- rious refinements of observation and calculation are introduced, but the general principle of the ojjeration is the same as has been described. Barometrical measurements of heights are only appro.ximate, since the moisture and dryness of the air, the wind, and various other atmospheric phenomena cause variations in the readings re- corded, and no formula can possibly be devised that will embrace all these sources of error. •Simultaneous observations, with barometers ad- justed to the same standard, give the most re- liable results. For a full discussion of the methods of measuring heights by trigonometrical leveling, precise leveling, and barometric observ-a- tions, the reader nwy consult Johnson, Theory and Practice of Surceying (New York, 1900). See Surveying. HYBA'CETTM (Neo-Lat., from Gk. Bpa?, hy- rax, mouse; connected with Lat. sorex, shrew- mouse). A peculiar substance found in the crev- ices of the rocks of Table Mountain. Cape of Good Hope. It is one or more of the e.xerements of the Cape hyrax (Hyrax capensis) . Hyraceum is a blackish-brown viscid material, not unlike soft pitch, having a strong and offensive taste, not unlike castoreum. for which it has been used as a substitute in medicine, though now obsolete. At one time so large a quantity was found as to suggest the idea of its being used as a manure, but Iho sufiply was soon exhausted. HYRAC'ODON (Neo-Lat., from Gk. !lpa|, hyrax, mouse + i55oi/s, odous, tooth). A primi- tive fossil rhinoceros found in the Miocene rocks of Western America and Europe. See Rhi- NOOERO.S. HY'RACOTHE'RITJM (XeoLat., from Gk. Upa^. hyrn.r. iiioise + g-^piov, thi'rion. diminii- tive of Slip, thrr, wild beast). .
extinct four-
tr.cd ungulate mammal of the size of a fox, gen- erally considered as an ancestral horse, remains of which are found in the Lower Eocene deposits of Europe and Western North America. See Horse. Fossil. HY'RAX (Neo-Lat., from Gk. PpaJ. mouse). A general name for a suborder (LTyracoidea) of small ])eculiar ungulate maunnals comprised in a Vol. X— 27. single genus and family (I'rocavia, Procaviidae), whose species are locally called 'conies,' 'damans,' and 'rock-rabbits.' Some fourteen species are known in .Southwestern Asia, ami in Eastern and Southern Africa. Although having the size and superficial appearance of rodents, and long so con- sidered, Cuvier pointed out their essential agree- ment, in dentition and anatomical characters, with the ungulates. The molars are quite similar to those of the rhinoceros, but the up|H-r jaw has two incisors curving downward, and during youth two very small canines, the lower jaw four inci- sors without canines. The skull, also, and other bones resemble those of the rhinoceros. The muzzle is short and pointed ; the ears short and round. The ribs are more numerous than even in the rhinoc- eros — 21 pairs, a numl)er exceeded in no quad- rupeds except the sloths, whereas no rodent has more than 15 pairs. The toes are united by the .skin, as in the elephant and rhinoceros, and are roiuid and soft, merely protected in front by a broad nail, which does not reach the ground. The legs are short. The tail is a mere tubercle. Their bodies are clothed with thick, uniformly dark- brown hair, except that it is discolored around a curious gland near the middle of the back, which is naked in several si)ecies. The habits of all the conies (except the tree- hyraces) are much alike. The typical Abyssin- ian species live in rocky or stony jilaces, in com- munities, like rabbits, and make their lionies in holes under rocks or in a rocky watercourse. They seem to be mainly nocturnal and feed at night or in the early morning on leaves and young shoots of trees and bushes. In daytime the}- lie on rocks in the shade until toward noon, when they are likely to retire to their holes. They are" very timid, and disappear when they arc "in the least danger. The only sound they seem to make is a shrill squeak when suddenly alarmed. This description will remind the reader of the closely similar behavior of the pikas (q.v. ) of the Rocicy Mountains, often called 'conies.' Mosely speaks of 'a short, hissing noise,' as the alarm cry of the Cape liyrax. All climb about smooth rocks with wonderful agility, which is explained by soft, almost suction-giving pads on the soles of their feet. (Consult Schweinfurth, Heart of Africa, vol. !., Leipzig, 1878.) The species longest known is the only Asiatic one (Procaritt ffyrica) , which inhabits Arabia, Syria, and Palestine, and is the aninuil called 'cony' in the ordinary version of the Bible, for which the Syrian name is 'daman.' It was among those animals prohibited to the Israelites under the mistaken belief that they chewed the cud: but they are now eaten by the .rabs, though not regarded as very jialatable by Europeans. Sev- eral species inhabit .Abyssinia and East A' ica, down to Mozambique; and Cape Colony and Natal are the home of a kind (Procavia Capen- sis) having very fine, soft, brown fur, with the spot on the back black, which is familiar to the English colonists under the names 'rock-badger' and 'rock-rabbit,' and to the Dutch as 'dassc.' They are often tamed as pets. Three species of the genus Pendrohyrax. which live in East and West Equatorial Africa, differ de- cidcdlv from other conies by (he habit of spending their lives and making their breeding nests in holes in trees. These three species agree in that the females have but a single pair of teats (other hyraces liave three pairs) , and the West Coast one
