Each huge globe of blinding whiteness was as it were clutched, compressed in a systole that was followed by a transitory diastole, and again a systole like a tightening grip, darkness, light, darkness, in rapid alternation.
Graham became aware that this strange behaviour of the lights had to do with the people below.

The appearance of the houses and ways, the appearance of the packed masses changed, became a confusion of vivid lights and leaping shadows.

He saw a multitude of shadows had sprung into aggressive existence, seemed rushing up, broadening, widening, growing with steady swiftness--to leap suddenly back and return reinforced.

The song and the tramping had ceased.

The unanimous march, he discovered, was arrested, there were eddies, a flow sideways, shouts of "The lights!" Voices were crying together one thing.