An old, old book about how to sing. Clearly the author believes what is being discussed, but some of the concepts would have been difficult if not impossible to prove at the time - such as breath being expelled in "whirling currents".
But you get a feel for what a master singer goes through:
"When I, for instance, was learning the part of Isolde, I could without weariness sing the first act alone six times in succession, with expression, action, and a full voice. That was my practice with all my rôles. After I had rehearsed a rôle a thousand times in my own room, I would go into the empty theatre and rehearse single scenes, as well as the whole opera, for hours at a time. That gave me the certainty of being mistress of my resonances down to the last note; and very often I felt able to begin it all over again. So must it be, if one wishes to accomplish anything worth while."
And:
"All the applause in the world cannot repay me for the sacrifices I have made for art, and no applause in the world is able to beguile me from the dissatisfaction I feel over the failure of a single tone or attempted expression."