H YD 



H YD 



of seven stars in the Bull's head, famous 

 among the poets for causing rain. 



HY' ALINE (vaXop, glass). Of a glassy, 

 thin, and semi-transparent substance. 

 The pellucid substance which determines 

 the spontaneous fission of cells. 



HY'ALITE {va\o9, glass). A siliceous 

 mineral occurring near Frankfort on the 

 Maine, in fissures in vesicular basalt and 

 basaltic greenstone, and employed by 

 lapidaries for ring-stones. 



HYALCE'IDiE (uaXo?, glass). A fa- 

 mily of Pteropods in the systems of 

 Cuvier and Lamarck, named from the 

 genus hyaloea, which is remarkable for 

 the delicacy and transparency of the 

 shell. 



HYBERNA'CULUM. Literally, a place 

 to winter in; a term fancifully applied 

 by Linnaeus to the bud of a plant, because 

 it protects the young and tender enclosed 

 parts during the winter. 



HYBERNATION {hyherna, winter- 

 quarters). A reptil e ^^ ^ te of the func- 

 tions, which occurs m some animals in 

 winter, as the bat, hedge-hog, dormouse, 

 hamster, &c. Compare Diumation. 



HY'BRID (hybrida, a mongrel). In 

 Botany, a plant produced by artificial 

 fecundation ; i. e. by crossing two dis- 

 tinct species of the same genus, or two 

 varieties of the same species. In a few 

 cases, mule plants have been artificially 

 obtained from individuals of different 

 genera. 



HYDATID {vdariv, a vesicle). A term 

 applied to several species of entozoa, or 

 parasitic animals, which have a distinct 

 independent vitality. 



HYDR-, HYDRO- {{idayp, water). A 

 Greek prefix generally denoting the pre- 

 sence of water in definite proportions ; 

 but, owing to the changes of nomencla- 

 ture, it sometimes denotes the presence of 

 hydrogen in certain chemical compounds. 

 In a few of the following terms it relates 

 to the hydra or fresh-water polyp : — 



1. Hydra {v6pa, hydra). A fresh-water 

 polyp, common in the ponds and clear 

 •waters of our own country, and affording 

 an excellent example of the structure of 

 the Acrita, being destitute of any percep- 

 tible trace of nervous substance, of mus- 

 cular fibre, of a vascular system, or of 

 reproductive apparatus. 



2. Hydra (in Astronomy). The Water- 

 snake ; a southern constellation, consist- 

 ing of sixty stars. 



3. Hydr-acids. Hydro-acids; a class 

 of acid compounds, into which hydrogen 

 enters as the supposed acidifying prin- 



169 



ciple, as the hydro-chloric, the hydro- 

 cyanic, &c. See Oxacids. 



4. Hydr-argillite (apytXAoc, clay). Na- 

 tive phosphate of alumina, erroneously 

 supposed to consist of alumina and water. 



5. Hydrates. Chemical compounds of 

 bases and water, still retaining the solid 

 form, as sulphur, soap, &c. These are 

 also termed hydr-oxures and hydro-oxides. 

 When there is more than one atom of 

 water, prefixes are employed, as bin- 

 aqueous, ter-hydrate, &c. 



6. Hydr-aulics (auXif, a pipe). That 

 branch of Natural Philosophy which in- 

 vestigates the laws by which fluids in 

 motion are regulated, and consequently, 

 the construction of machines in which 

 water is employed as a moving power, or 

 by which that fluid is put in motion. 



7. Hydraulic Press. An apparatus 

 contrived or applied by Mr. Bramah, for 

 illustrating the hydrostatical law of the 

 equal pressure of liquids in all directions. 

 A small quantity of water is driven by- 

 sufficient pressure into a vessel already 

 full, and provided with a moveable sur- 

 face or piston of great size. Under such 

 circumstances something must give way ; 

 the great surface of the piston accumu- 

 lates the pressure on it to such an extent 

 that nothing can resist its violence. The 

 apparatus is employed in compressing 

 bodies, in lifting weights, in raising trees 

 from the soil, or piles from the beds of 

 rivers. 



8. Hydraulic Ram, or Water Ram. A 

 hydraulic machine for raising water by 

 means of its own impulse, invented by 

 Mr. Whitchurch, and improved by Mont- 

 golfier. 



9. Hydr-iodic acid. A gaseous com- 

 pound of hydrogen and iodine, procured 

 by the mutual decomposition of iodide of 

 phosphorus and water. 



10. Hydro-henz amide. A colourless 

 substance obtained by placing hydrate of 

 benzoile in a solution of ammonia. 



11. Hydro-branchia {/Spayx'a* gj^s). 

 Under this term Lamarck includes 

 the Nudibranchia, Scutibranchia, and 

 Tectibranchia of Cuvier, together with 

 certain genera, wliich are arranged in a 

 section. Se Pneumobravchia. 



12. Hydro-bromic acid. A gaseous 

 compound of hydrogen and bromine, 

 obtained by the mutual decomposition 

 of bromide of phosphorus and water. 



13. Hydro-carbon. A combustible mi- 

 neral substance found in the interstices 

 of lignite. A com.pound of hydrogen 

 and carbon : these elements combine in 



I 



