I promised to check in from time to time as we finished our conversation.
I may ask you to turn your head from time to time.
The furrowed surface of the earth gives the land-area a star-shaped figure, which may from time to time have varied in outline, but in the main has been permanent.
The boundaries of the Transvaal have varied from time to time.
This gives to it unity and definiteness, and renders superfluous the attemps that have been made from time to time to define the limits which divide geography from geology on the one hand and from history on the other.