© 1955 by Oxford University Press
TWO PROPERTIES OF SPHERICAL HARMONICS
( St. John's College Cambridge )
The integral of the square of the gradient of a solid harmonic over a sphere is evaluated; the corresponding integral for the second derivatives is also evaluated, and the results are applied to an integral that includes the elastic energy in a strained sphere and the rate of dissipation in a viscous sphere.
A natural definition of the irregularity of a function over a sphere leads to the conclusion that the irregularity is stationary for small variations of the function when the function is a surface harmonic and that the irregularity of any function is greater than that of the lowest term in its expansion in surface harmonics.