Oboist Geoffrey Browne writes that:
I cannot help thinking that the pumping action of the foot may have been very disturbing and that, for very long passages, the cor anglais player may have had to ask a trusted colleague to take over the pumping for a short time so as not to disturb the embouchure. It had also occurred to me that the playing of concertos might be difficult because the foot-pumping could be awkward when standing up, and impossible if the player had only one leg. There could have been a very long air pipe going off-stage and into the wings where the pumping could be concealed from view.The extent of a player's breath is a constant concern in music for wind instruments, and composers make demands for extended tones or breathless passage work at their own peril. A few players have mastered the art of circular breathing, most famously Harry Carney, baritone saxophonist in the Ellington Band, who would hold a single tone long past the rest of the ensemble, in a kind of solo cadenza reduced to a single, very long, fermata. Circular breathing is, however, a fixed part of wind instrument technique in many parts of the world, and is particularly useful when playing a drone. The Australian dijeridu, an instrument that has justifiably gained some popularity, is at its best when played with a circular technique. The late virtuoso South Indian flutist, T. Viswanathan, told a hilarious story about an itinerant Mukha Veena player, who showed up to pay his respects at the death of Viswa's sister, the great dancer Balasaraswati. This Mukha Veena player sat at the floor, asked for one cup of water and an additional empty cup, whereupon he took out his Mukha Veena and a plastic straw, and proceeded to play, using circular breathing and simpultaneously drinking the water in one cup out of one side of the mouth and emptying it into the second cup out of the other side.
It may be that for very long cor anglais solos the player had several air pipes in his mouth and that several of his colleagues operated foot pumps so as to make sure he did not run out of air. Maybe they took it in turns to work the foot pumps as each colleague became exhausted. It would have been necessary to keep careful watch over the cor anglais player to make sure he did not become over-inflated. As a safety precaution the cor anglais player may also have had a foot pump with an air line going into the mouths of his assistants so he could signal his distress if either he was receiving too much or too little air.
Seemless and noiseless circular breathing is, unfortunately, a rare technique among most players of western instruments, and many of those who do use circular breathing techniques do so at the cost of an unsteady tone, extraneous noises, or a distracting visual presentation. Electronic technologies -- delay lines and the like --, as successors to Samuel's mechanical Aerophon(e), may solve the problem in some cases, but there will probably always be a place on stage for the artist able sustain a tone for a while longer than the audience can hold its collective breath before exploding into awes of relief and well-deserved applause.
* The original, French, name seems not to include the "e" on the end. Aerophor(e), with an "r", would connect it to the undersee diving device as well as a machine used in infant care, and would convey the Greek root sense of an air supply. Musicians, of course, would take kindly to a device with a phon(e) ending. English language sources sometimes include the final "e", and among these, the Harvard Concise Dictionary of Music and Musicians demands it and scolds Strauss for using the -phon form. But AFAIC, I'll go with Strauss and the HCDM&M can take its pedant final "-re" and shove it somewhere where the Aerophon will not blow.