In 1984, most jets appeared (from their collimation and brightness evolution) to be confined, but we could not agree how. Few of the X-ray environs of well-imaged radio sources had been detected. The exceptions (e.g., M87, Cygnus A) were exceptionally gas-rich systems with high inferred values of . Given these few, generous, X-ray detections and high upper limits, there was good reason to hope that FR I jets with modest minimum pressures are confined thermally by galactic atmospheres. But some FR II jets were clearly over-pressured relative to X-ray limits on surrounding free-free emission, and geometry alone made it difficult to explain this away by relativistic beaming. Magnetically-assisted collimation of current-carrying jets was seen as an escape from this dilemma.
Since then, we have seen how light, hypersonic FR II jets can be significantly over-pressured relative to the ambient medium by protectively cocooning themselves (Loken et al. 1992; Cioffi & Blondin 1992). Magnetic collimation of such jets not only seems inessential, but undesirable-MHD models show that it inhibits lobe and filament formation, in conflict with the data (Clarke, these Proceedings), especially as filamentation is so widespread (Perley, Dreher, & Cowan 1984; Fomalont et al. 1989; Hines, Owen, & Eilek 1989; O'Donoghue, Eilek, & Owen 1990; Bridle et al. 1994a; Swain, Bridle & Baum, these Proceedings).
In contrast, the limits for the extended X-ray emission around some ostensibly confined FR I jets have tightened (Birkinshaw & Worrall, these Proceedings). These large sources show uncomfortably little evidence for the putative confining medium-just as it assumes new importance to the dynamics of decelerating-jet models. Are jets in FR I and FR II sources trading places as the vexing problem? For reassurance that this may not be so, see Burns (these Proceedings) and Owen et al., (these Proceedings). The evidence for static confinement may also be worth re-examining in the context of sheared flows-are the collimation measures robust and the brightness-radius ``adiabats" appropriate?
One constant through the confinement debate has been the M87 jet: highly one-sided, significantly over-pressured (Owen, Hardee, & Cornwell 1989), and not obviously self-cocooned. Its sharp features had been seen as an obstacle to interpreting it as a Doppler-enhanced jet, but Bicknell & Begelman (these Proceedings) show that the statistics of relativistic aberration make this solution less contrived, and the proper motions strongly support it (Biretta, these Proceedings).