Time domain

To put the above equations in the time domain, it is necessary only to get $\omega$ into the numerator and then replace $-i \omega$ by $\partial / \partial t$.For example, the 15$^\circ$, retarded, $v = \bar v$ equation from Table .5 becomes  

$${ \partial^2 \over \partial z \ \partial t } \ Q \eq {v \over 2 }\ { \partial^2 \ \over \partial x^2 } \ Q$$ (21)

Interpretation of time t for a retarded-time variable Q awaits further clarification in chapter .