"John, in a minute or two I shall wish you to go and get some wood.

You can be getting your things ready to be left." "Mary, it is almost time for your lesson.

You had better put Dolly to sleep and lay her in the cradle." "Boys, in ten minutes it will be time for you to go to school.

So do not begin any new whistles, but only finish what you have begun." On the same principle, if boys are at play in the open air--at ball, or skating, or flying kites--and are to be recalled by a bell, obedience to the call will be made much more easy to them by a preliminary signal, as a warning, given five minutes before the time.
Of course, it will not always be convenient to give these signals and these times of preparation.

Nor will it be always necessary to give them.