The Ethereal Interlude is my name for the smoothly evocative section in Dazed and Confused right before the bow solo for every performance of the song from late 72 up through the last performance at Earls Court in May of 1975. Musically the section started with a deviation from the furious guitar soloing and rhythmic workout of the previous section where the band backed off abruptly and smoothed themselves out creating a calm eerie mood. It served to set the table for the bow solo to follow where the disconnect between the fury of the heavier sections and the creepyness of the spaceout sections was greatest. The section's end is defined at the point where Jimmy first uses the bow.
The first appearance of the Ethereal Interlude started in the last few dates of the Summer 72 US tour where Page dips his toe in the water trying to set the mood correctly. They were very short and naked at this point though and the section really wouldn't start to take shape until late in the year.
By Decmember of 72 the song was developing nicely and Jimmy had started playing the altertating asscending and descending melodic guitar line that would eventually develop into one of the central elements of Achilles Last Stand, which wouldn't appear on an album until Presence nearly four years later. Jimmy set the mood and Jones and Bonham followed and accented him. Over this hypnotic backdrop Plant tried singing 'Cowgirl in the Sand' by Neil Young for a few shows, but soon settled in to the pattern of singing Scott McKenzie's 'San Fransisco', which he sang for all of the performances from December of 72 through the first leg of the 75 tour. Starting with the second leg of the 75 tour Plant switched to singing 'Woodstock' by Joni Mitchell as well as a few random one off performances of other songs, such as 'I Shot the Sherriff' by Bob Marley, 'For What It's Worth' by Buffalo Springfield and 'Spanish Harlem' by Ben E King. San Fransisco returned for two of the Earls Court performances which were the last shows where Dazed and Confused was ever performed by Led Zeppelin.