Fox Broadcasting Co.’s “The Adventures of Brisco County Jr.” lassoed healthy ratings in Nielsen overnights on Friday, finishing second with its 8-10 p.m. premiere.The Warner Bros. Western averaged an 8.3 rating, 15 share in Nielsen major markets. CBS, meanwhile, didn’t help itself by flopping “The Building” and “The Boys;” the hour slumped to fourth place in the time period. NBC also looked OK with the premiere of “Trade Winds,” the first of its “great escapes” serials. The show was pre-empted in several major markets but averaged an 8.0/14 in the markets in which it aired, according to NBC research. CBS got off to a solid start Thursday with the new primetime soap “Angel Falls” (10.5/19), which captured the web’s highest share in its 10 p.m. time period since the final episode of “Knots Landing” May 13. More significantly, the share was equal to “Knots’ ” average during the 1992- 93 season and seemed to tap into the same audience, with a 20 share among women 25-54 and greater national appeal than its overnight-market average. “Seinfeld” moved comfortably into its new 9 p.m. slot with a 12.1/20, topping every “Cheers” performance there since May 27. “Eye to Eye With Connie Chung” ( 11.8/20) continues to build, having achieved ratings highs the past two weeks.