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When is large the quantity in [ ]

vanishing when .

Thus, making use of we have for the magnetic energy

Now by (17) we have at the surface of the ellipsoid

Hence the total electromagnetic energy of the ellipsoid is

. | (23) |

Here we must remember that .

(A) *Energy of Heaviside Ellipsoid*. If we put = S and make S large we have

(24) |

This corresponds to the Heaviside ellipsoid, for when , . The energy of the same ellipsoid at rest is

(B) *Energy of a Sphere.* Putting we have , and thus

. | (25) |

If is small compared with we have

It will be found that as far as the magnetic energy is

as has been found by Mr. Heaviside.^{[1]} It follows from this

- ↑ 'Electrical Papers' vol. ii. p. 505.