quickening

If the following guide lose his distance from the one leading (which can only happen by his own fault), he will correct himself by slightly lengthening or shortening a few steps, in order that there may not be sudden quickenings or slackenings in the march of his platoon.

It may indeed be said that these days brought on a high quickening of Maisie's direct percptions, of her sense of freedom to make out things for herself.