HAL 



rals ; tasteless ; specific gravity from 

 2.2 to 3.3. 



HA'LLOSITE. An earthy mineral of a 

 white colour with a slightly bluish 

 tinge, occurring with ores of lead, 

 zinc, and iron. Thus named by 

 Berthier in honour of M. Omalius 

 d'Halloy. 



HALT'EBES. (aXr^ee, Gr. halteres, 

 Lat.) The poisers, so named from 

 their supposed use in balancing the 

 body, or adjusting with exactness 

 the centre of gravity when the 

 insect is flying. In those insects 

 which compose the order Diptera, 

 we meet with two organs, con- 

 sisting of cylindrical filaments, 

 terminating in a clubbed extremity; 

 one arising from each side of the 

 thorax, in the situation in which 

 the second pair of wings originate 

 in those insects that have four 

 wings; these are called halteres. 

 "Whatever may be their real utility, 

 they may still be regarded as rudi- 

 ments of a second pair of wings. 

 HA'MITE. (from hamus, Lat. a hook.) 

 A genus of fossil multilocular hook- 

 formed shells. Parkinson states 

 that the hamite has no evident 

 siphunculus, but this is a mistake ; 

 the siphuncle of the hamite, like 

 that of the ammonite, is placed on 

 the back, or outer margin of the 

 shell, and in some species this 

 marginal siphuncle has a keel- 

 shaped pipe raised over it. The 

 external shell is fortified by trans- 

 verse folds or ribs, which serve to 

 strengthen both the outer and the 

 air chambers. The hamite is 

 sometimes found of large size, more 

 especially that species known as 

 Hamites grandis ; some of them are 

 of the diameter of a man's wrist. 

 HAPLACA'NTHTJS. The name assigned 

 to a fossil fish of the old red sand- 

 stone, one species of which has been 

 described by Agassiz, namely, H. 

 Marginalis. 



HAEDNESS. In mineralogy, one of 

 the physical or external characters 



[ 210 ] EAR 



used in determining minerals. To 

 Prof. Mohs we are indebted for a 

 scale easily formed, and at the 

 same time distinct and accurate. It 

 is as follows : 



1. Talc, of a white or greenish 

 colour. 



2. Rock-salt, a pure cleavable 

 variety ; or gypsum uncrystallized, 

 and only semi- translucent. 



3. Calcareous spar, any cleavable 

 variety. 



4. Fluor spar, presenting good 

 cleavage. 



5. Apatite, the asparagus stone 

 from Saltzburgh. 



6. Adularia, any perfectly cleav- 

 able variety. 



7. Rock crystal, limpid and trans- 

 parent. 



8. Topaz, any simple variety. 



9. Corundum stone from Bengal, 

 which affords a smooth surface 

 when fractured. 



10. The diamond. 



In employing this scale, we en- 

 deavour to find the degree of hard- 

 ness of a given mineral by trying 

 which number of the series is 

 scratched by it ; or, still better, by 

 passing with the least possible force 

 the specimens under comparison 

 over a very fine file. Prom the 

 resistance these bodies afford to the 

 file, from the noise occasioned by 

 their passing over it, and from the 

 quantity of powder left on its sur- 

 face, their mutual relations in 

 respect to hardness are deducible 

 with great correctness. When, 

 after repeated trials, we are satisfied 

 which member of the scale the 

 mineral is most closely allied to, 

 we say its hardness is equal to 

 seven, (suppose it to be rock crys- 

 tal) and write after it H. = 7*0. 

 If, however, the mineral under ex- 

 amination do not exactly correspond 

 with any one member of the scale, 

 but is found to be between two of 

 them, we say H. = 7'5, or 7'75 if 

 it approximate to the next higher 



