178.

With the value [eqn:(320)] (320) obtained for $𝖨$ the total energy absorbed by the oscillator in an element of time $dt$ from the radiation falling on it is found from [eqn:(249)] (249) to be $\frac{\pi dt}{cL}\int {\sin }^2\theta d\Omega (𝖪{\cos }^2\psi +{𝖪}^{\prime }{\sin }^2\psi ).$ Hence the oscillator absorbs in the time $dt$ from the pencil striking it within the conical element $d\Omega$ an amount of energy equal to $\frac{\pi dt}{cL}{\sin }^2\theta (𝖪{\cos }^2\psi +{𝖪}^{\prime }{\sin }^2\psi )d\Omega .\mathrm{\backslash Label}[eqn](321)\text{upshape (321)}$