Take another look at the sentence:
Watching the second hand sweep the clock, the end of the boring lecture
on the French Revolution seemed as if it would never arrive.
Watching the second hand sweep the clock, a participle phrase, comes right before end, an illogical target. Students, not an end, watch the clock! Before you continue, review the rules for misplaced and dangling modifiers.
Go back to the sentence to try again.