After exorcising his rock'n'roll demons and splitting up Loop at the turn of the decade, guitarist Robert Hampson (concurrent with a short stay in Godflesh) devoted himself to a campaign to promote inertia by any means necessary. Under the guise of Main, Hampson and his collaborator, guitarist Scott Dowson, explore ambient structures that edge imperceptibly from tranquility to clamor, manifesting as stealthy a progression as one of Brian Eno's abstract film scores. Main has a bit of common ground with ambient techno-largely a shiatsu-like body consciousness-but the group's edifices allow for the introduction of more real ambient sound than most.

The always mysterious and now-defunct Main is at its most aggressive on Hydra and Calm (compiled with a bonus track, "Thirst," as Hydra-Calm), leaning hard into the array of flangers and phasers that provide the elegant dislocation of bass-heavy tracks like "Flametracer" and "There Is Only Light." It would be misleading to insinuate that the band was playing "rock" at this stage, but only a few of these pieces (notably the opalescent 20-minute "Thirst") luxuriate in languor to the fullest. While Firmament operates within the realm of songform, the influences are clearly more diffuse — a bit of 23 Skidoo-styled percussive wankery used to underpin an array of primitive electronics that seem to have been appropriated from Cabaret Voltaire's Sheffield basement. Abrasive, but not much more.

A note on the back of Motion Pool heralds a push into "drumless space," a Jello-floored realm that's actually quite soothing to infiltrate. The album's pieces are distinct and compact — if considerably more formless than what had come before. Hampson's vision is not yet fully realized: the self-conscious "VII" might as well have been lifted whole from one of those old sound effects records that clutter thrift-store bins. But when the pieces connect (or more precisely, when they hang just the right distance apart), there's a sense of indigenous menace — particularly palpable on "Rail" and "Crater Scar" — that's positively enthralling.

Firmament II ushers in a new era, wherein all of the rock (and most of the music) is removed from Main's sphere of influence. The disc consists of a single piece, mottled with subtle clattering, that refuses any sort of personal connection. Oddly enough, the album makes for compelling enough ancillary listening to provoke sequential spins-it sure beats those white-noise generators when it comes to drowning out the outside world.

The half-dozen EPs that emanated from the Main camp in 1995 are to be taken as a piece — as evidenced by their subsequent compiling in the minimal-yet-luxurious Hz box. If experienced with too much of a time lag, the records tend to blend together, but immersion accentuates the subtle differences between, say, the Terry Riley-like harmonic drones that dominate Corona (two long, incrementally intensifying pieces) and the more strident Reich-isms consolidated in the three movements of Terminus. When Hampson strives for industrial audio vérité (as on sections of the fragmented Maser), he fails to provide a trenchant format for the urban sounds he so lovingly recreates. But when he transfigures those same factory scenes into three-dimensional form (as on the icily beautiful Haloform), Hampson makes a case for atmosphere as an end in itself.