As he rehearses, the conductor, surrounded by the physical sound of the work,checks his own concept of the music, comparing it with the actual music. In those parucular instances where the two do not fit, he must alter one or the other. It is essential that the two, the concept and the actnality, run amicably along. In addition,there are instances,such as the lengthy oboe solo in Strauss's Don Juan, where the prudent conductor who is foruinate enought to possess a highly sensitive oboe player permits him to "have his head," acting almost as an accompanist rather than a leader.