The polyhedral aggregates were abundant and reached considerable dimensions. The crystallizing power of the cadmium however, seems to be less, so that the only crystals suitable for measurement were extremely minute. The largest individuals were barrel-shaped, like those of zinc and resembled little piles of basal plates. Their side planes are not infrequently uneven and bent, probably as the result of the softness and great ductility of the metal. Only the most minute crystals show pyramidal planes of comparative perfection. These are well suited for a microscopic examination, but their small size renders their measurement on a reflecting goniometer a matter of difficulty. After a careful search two crystals were secured which, although they had a diameter of only one third of a millimeter, from their microscopic appearances promised good results. Their planes however were found to give compound reflections and a somewhat disappointing variation in corresponding angles. On the best crystal three zones were measured as follows: (normal angles) Zone I Zone II Zone III 0001 : 01ī1 = 62° 35′ |0001 : 10ī1 = 62° 4′ |0001 : 1ī01 = 62° 29′ 0001 : 01ī0 = 89° 50½′| | 0001 : 01īī = 118° 57′ |0001 : 10īī = 118° 28′| The second crystal was much less satisfactory, since values for the angle between the base and pyramid (0001): (01ī1) were obtained which varied all the way from 61° 2′ to 63° 43′. These measurements must therefore be regarded as of little or no value. If we average the readings for this angle on the first crystal we obtain 62° 23′, from which ̲a : ̲c = 1 : 1.6554. A comparison of the axial ratios of the four rhombohedral and four holohedral hexagonal elements gives the following: { Bismuth ̲a : ̲c = 1 : 1.3035 (G. Rose, 1849). Rhombo- { Antimony ̲a : ̲c = 1 : 1.3235 (Laspeyres, 1875). hedral. { Tellurium ̲a : ̲c = 1 : 1.3298 (G. Rose, 1849). { Arsenic ̲a : ̲c = 1 : 1.4025 (Zepharovich, 1875). { Zinc ̲a : ̲c = 1 : 1.356425 (Williams and { Burton, 1889). Holohedral. { Beryllium ̲a : ̲c = 1 : 1.5802 (Brögger, 1884). { Magnesium ̲a : ̲c = 1 : 1.6202 (Williams, 1890). { Cadmium ̲a : ̲c = 1 : 1.6554 (Williams, 1891). Zinc appears from its axial ratio to belong rather to the rhombohedral group and this is the only one of the last four elements upon which the faintest indication of any divergence from a holohedral development of all of its forms has been observed. On crystals of this substance there is an occasional rhombohedral alternative of the faces of certain of the pyramids, although the crystals otherwise appear to be holohedral.[19]