Ralph Hartley

Ralph Vinton Lyon Hartley was an American electronics researcher whose work on radio circuits and communication helped establish an early mathematical measure of information.

Hartley entropy: A logarithmic measure of the information represented by a set of equally likely alternatives. Hartley’s 1928 paper gave this measure a central role in communication theory.
Hartley’s law: A formula assigning log₂(Nⁿ) bits to a sequence of n choices from N equally available symbols. It expresses Hartley’s central proposal for counting message information.
Harry Nyquist: A Swedish-American physicist and engineer whose work established foundational limits for telegraphy and signal transmission. Nyquist’s communications research overlapped with Hartley’s and informed later channel-capacity work.
A Mathematical Theory of Communication: Claude Shannon’s 1948 paper that formalized information theory and communication-channel capacity. Shannon’s paper transformed the problem Hartley had approached in his 1928 work.
Claude Shannon: An American mathematician and engineer who founded modern information theory. Shannon extended Hartley’s measure to account for probabilities and noisy channels.
Logarithm: The inverse operation of exponentiation, converting multiplication into addition. A logarithm makes the information in successive independent choices additive.
Ralph V. L. Hartley: The full name of Ralph Hartley, an American electronics researcher born in 1888. This name variant appears in technical and historical sources about his research.
Radio engineering: The engineering discipline concerned with generating, transmitting, and receiving radio-frequency signals. Hartley’s research grew from practical problems in radio communication.
Information theory: The mathematical study of information, its representation, transmission, and limits. Hartley’s work supplied an early quantitative foundation for this field.
Bit: A unit of information equal to the choice between two equally likely alternatives. Hartley’s measure can be expressed in bits when its logarithm uses base two.

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