BESSEL FUNCTION

This article appears in Volume V03, Page 823 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: BER-BLA

BESSEL FUNCTION , a certain mathematical relation between two variables. The Bessel

function

FUNCTION

\ of order m satisfies the differential equation _! + p j((p + (I P z I u = o, and may be expressed dp2 as the

series

SERIES (a Latin word from serere, to join)

`Dml 1- P2
2.2m + 2 /+
2 2.4.2m+2.2m+4 ... ; the

function

FUNCTION

of zero order is deduced by making In= o, and is equivalent to the

series

SERIES (a Latin word from serere, to join)

1-4 + ,v.4.
&c. O. Schlomilch
defines these functions as the coefficients of the power of t in the expansion of exp Zp(tt-'). The symbol generally adopted to represent these functions is Jm (p) where m denotes the order of the function. These functions are named after

Friedrich

FRIEDRICH, JOHANN (1836— )

Wilhelm Eessel, who in 1817 introduced them in an investigation on Kepler's Problem. He discussed their properties and constructed tables for their evaluation Although Bessel was the first to systematically treat of these functions, it is to be noted that in 1732 Daniel Bernoulli obtained the function of zero order as a solution to the problem of the oscillations of a chain suspended at one end. This problem has been more fully discussed by Sir A. G. Greenhill. In 1764 Leonhard

Euler

EULER, LEONHARD (1707-1783)

employed the functions of both zero and integral orders in an

analysis

ANALYSIS (Gr. avci and Meta, to break up into parts)

into the vibrations of a stretched membrane; an investigation which has been considerably developed by Lord Rayleigh, who has also shown (1878) that Bessel's functions are particular cases of Laplace's functions. There is hardly a branch of mathematical physics which is independent of these functions. Of the many applications we may notice:Joseph

Fourier

's (1824) investigation of the motion of heat in a solid cylinder, a problem which, with the related one of the flow of electricity, has been developed by W. E. Weber, G. F. Riemann and S. D.

Poisson

POISSON, SIMEON DENIS (1781-1840)

; the flow of electromagnetic waves along wires (Sir J. J. Thom-son, H. Hertz, O. Heaviside); the diffraction of light (E. Lommel, Lord Rayleigh, Georg Wilhelm Struve); the theory of elasticity (A. E. Love, H. Lamb, C. Chree, Lord Rayleigh); and to hydrodynamics (Lord Kelvin, Sir G. Stokes).
The remarkable connexion between Bessel's functions and spherical harmonics was established in 1868 by F. G. Mehler, who proved that a simple relation existed between the function of zero order and the zonal harmonic of order n. Heinrich Eduard Heine has shown that the functions of higher orders may be considered as limiting values of the associated functions;
this relation was discussed independently, in 1878, by Lord Rayleigh.
For the mathematical investigation see SPIP'RICAL HARMONICS and for tables see TABLE, MATHEMATICAL.
See A. Gray and G. B.

Matthews

STANLEY
_1824_1889_.html">MATTHEWS,
STANLEY
(1824-1889)

, Treatise on Bessel's Functions (1895); Encyclopddie der math. Wissenschaften;F. W. Bessel, Untersuchung des Teils der planetarisehen Storungen (1824).

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