Forth to frolic

Vermont--

Welcome to A2k.

Can you give a bit of context for the sentence? From what you've presented I'd guess the author is comparing the leaking gas fumes to dancers or vandals, disporting themselves in public, but without some context that can only be a guess.

Context
Exactly at eight Hickey--Mooney, of the vaudeville team (unbooked) in the flat across the hall, would yield to the gentle influence of delirium tremens and begin to overturn chairs under the delusion that Hammerstein was pursuing them with a five-hundred- dollar-a-week contract. Then the gent at the window across the air- shaft would get out his flute; the nightly gas leak would steal forth to frolic in the highways; the dumbwaiter would slip off its trolley; the janitor would drive Mrs. Zanowitski's five children once more across the Yalu, the lady with the champagne shoes and the Skye terrier would trip downstairs and paste her Thursday name over her bell and letter-box--and the evening routine of the Frogmore flats would be under way.
John Perkins knew these things would happen. And he knew that at a quarter past eight he would summon his nerve and reach for his hat, and that his wife would deliver this speech in a querulous tone

Vermont--

Delightful writing--except for :



because the "nightly gas leak" can't frolic while the leaking fumes can.

While I'm being critical I think the leaking fumes are more likely frolicing in the air shaft than the "highway" (which one presumes is outside this very interesting building)