Optical Pyrometer
An instrument for measuring the temperature of heated material by comparing the intensity of
light emitted with a known intensity of an incandescent lamp filament.

Order Hardening
A lowtemperature annealing treatment that permits
matrix, which greatly impedes dislocation motion.

OrderDisorder Transformation
A phase change among two solid solutions having the same crystal structure, but in which the
atoms of one phase (disordered) are randomly distributed; in the other, the different kinds of
atoms occur in a regular sequence upon the crystal lattice, that is, in an ordered arrangement.
Compare with dissociation .

Orsat Analyzer
An atmosphere analysis device in which gases are absorbed selectively (volumetric basis) by
passing them through a series of preselected solvents.

Object Oriented Language
A computer program that uses onscreen objects, called icons, to represent commands. A movable device, such as a mouse or trackball, is used to move an arrow or other pointer to the icon; then a button is pressed to carry out the function indicated by the icon.

Octal to Decimal Conversion
Conversion of numbers in the octal number system to numbers in the morefamiliar decimal number system. This is done by expressing the octal number serially in powers of eight. Thus, octal 12 = (1 × 81) + (2 × 80) = 8 + 2 = decimal 10.

Odometer
An electromechanical device that indicates the speed of, and distance covered by, a
moving vehicle or robot. Some such devices give a constant position indication, via mathematical integration of the measured velocity (speed and direction), relative to time. It can function in one, two, or three dimensions.

Ohm’s Law
The statement of the relationship among current, voltage, and resistance. In a directcurrent circuit, current varies directly with voltage and inversely with resistance: I = E/R, where I is the current in amperes, E is the voltage in volts, and R is the resistance in ohms. For alternating current, Ohm’s law states that I = E/X = E/Z, where X is reactance and Z is impedance.

