which doth make
  The meat it feeds on,

a desire that cannot be quenched, yet will not despair.  Then, at the lowest ebb of the sweet agony, an ecstasy of hope, a wildly blissful contemplation of a promise of reward.  If I depart here for a brief space from my announced purpose not to analyze the music in the manner of the Wagnerian commentators, it will be only because the themes of the prelude are the most pregnant of those employed in the working out of the drama, because their specific significance in the purpose of the composer is plainly set forth by their association with scenes and words, and because they are most admirably fitted by structure and emotional content to express the things attributed to them.  The most important of the themes is that with which the prelude begins:—­

[Musical excerpt]

Note that it is two-voiced and that one voice ascends chromatically (that is, in half steps), and the other descends in the same manner.  In the aspiring voice there is an expression of longing; in the descending, of suffering and dejection.  We therefore may look upon it as a symbol of the lovers and their passion in a dual aspect.  After an exposition of this theme there enters another:—­

[Musical excerpt]

followed immediately by:—­

[Musical excerpt]

In the play the first of these two is associated with the character of the hero; the second with the glance which Tristan cast upon Isolde when she was about to kill him—­the glance which inspired the love of the princess.  Two modifications of the principal theme provide nearly all the rest of the material used in the building up of the prelude.  The first is a diminution of the motif compassed by the second and third measures, which by reiteration develops the climax of the piece:—­

[Musical excerpt]

The second is a harmonized inversion of the same short figure, preceded by a jubilantly ascending scale:—­

[Musical excerpt]

This is the expression of the ecstasy of hope, the wildly blissful contemplation of a promise of reward of which I have spoken.  Wagner tells us what the thing hoped for, the joy contemplated in expectation, is, not only in the drama, but also in an exposition of the contents of the prelude made for concert purposes.  He deserves that it shall be known, and I reproduce it in the translation of William Ashton Ellis.  After rehearsing the legend down to the drinking of the fateful philtre, he says:—­

The musician who chose this theme for the prelude to his love drama, as he felt that he was now in the boundless realm of the very element of music, could only have one care:  how he should set bounds to his fancy, for the exhaustion of the theme was impossible.  Thus he took, once for all, this insatiable desire.  In long-drawn accents it surges up, from its first timid confession, its softest attraction, through sobbing sighs, hope and pain, laments and wishes,