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The act of collimating; the adjustment of the line of the sights, as the axial line of the telescope of an instrument, into its proper position relative to the other parts of the instrument. Error of collimation, the deviation of the line collimation of an astronomical instrument from the position it ought to have with…

bounded by plane surfaces, symmetrically arranged, and each species of crystal has fixed axial ratios. See Crystallization.

lities. Dispersion of the optic axes (Crystallog.), the separation of the optic axes in biaxial crystals, due to the fact that the axial angle has different values for the different colors of the spectrum.

Above or outside of the endoskeleton; epaxial.

The first, or preaxial, digit of the hind limb, corresponding to the pollux in the fore limb; the great toe; the hind toe of birds.

Beneath the endoskeleton; hypaxial; as, the hyposkeletal muscles; -- opposed to episkeletal.

of crystallized bodies are viewed in converging polarized light; thus, a section of a uniaxial crystal, cut normal to the vertical axis, shows a series of concentric colored rings with a single black cross; -- so called because produced by the interference of luminous waves. -- Interference fringe. (Optics) See Fring…

A prefix signifying much or many; several; more than one; as, multiaxial, multocular.

oped beneath the medullary groove in the vertebrate embryo, and constitutes the primitive axial skeleton around which the centra of the vertebræ and the posterior part of the base of the skull are developed; the chorda dorsalis. See Illust. of Ectoderm.

A combining form denoting relation to, or situation near, the occiput; as, occipito-axial; occipito-mastoid.

a doubly refracting crystal, in the direction of which no double refraction occurs. A uniaxial crystal has one such line, a biaxial crystal has two. -- Optical circle (Opt.), a graduated circle used for the measurement of angles in optical experiments. -- Optical square, a surveyor's instrument with reflectors for l…

e crystallographic axes which determines the position of any plane; also, the fundamental axial ratio for a given species.

The first, or preaxial, digit of the fore limb, corresponding to the hallux in the hind limb; the thumb. In birds, the pollex is the joint which bears the bastard wing.

An extra first toe, or rudiment of a toe, on the preaxial side of the hallux.

An extra first digit, or rudiment of a digit, on the preaxial side of the pollex.

An order of marine Bryozoa, having a bilobed lophophore and an axial cord. The genus Rhabdopleura is the type. Called also Podostomata. See Rhabdopleura.

The preaxial bone of the forearm, or brachium, corresponding to the tibia of the hind limb. See Illust. of Artiodactyla.

double refraction is possessed by all crystals except those of the isometric system. A uniaxial crystal is said to be optically positive (like quartz), or optically negative (like calcite), or to have positive, or negative, double refraction, according as the optic axis is the axis of least or greatest elasticity for l…

One of group of two to four united cells which occupy the axial part of the ocelli, or ommatidia, of the eyes of invertebrates, and contain the terminal nerve fibrillæ. See Illust. under Ommatidium.

nes. Specif. (Crystallog.), one of the parts of a crystal into which it is divided by the axial planes.