Annoyed at the inopportune intrusion, Rob's first thought was to go back to the street and try another building; but, upon reflecting that the young man was not likely to remain long and he would soon be alone, he decided to wait.  So he walked to the edge of the roof and appeared to be interested in the scenery spread out below him.
"Fine view from here, ain't it?" said the young man, coming up to him and placing his hand carelessly upon the boy's shoulder.
"It is, indeed," replied Rob, leaning over the edge to look into the street.
As he spoke he felt himself gently but firmly pushed from behind and, losing his balance, he plunged headforemost from the roof and whirled through the intervening space toward the sidewalk far below.
Terrified though he was by the sudden disaster, the boy had still wit enough remaining to reach out his right hand and move the indicator of the machine upon his left wrist to the zero mark.  Immediately he paused in his fearful flight and presently came to a stop at a distance of less than fifteen feet from the flagstones which had threatened to crush out his life.
As he stared downward, trying to recover his self-possession, he saw the old gentleman he had met on the Lake Front standing just below and looking at him with a half frightened, half curious expression in his eyes.