The Latin phrase "Semper Dolens, Semper Dowland" was the motto of Elizabethan era Lutenist John Dowland. The phrase is cited by historians of music as the reason why John Dowland's last name should be pronounced to rhyme with "No-land" and not "Now-land." If it were pronounced to rhyme with "Now-land," it would not fit the rhyme scheme.
The phrase translates to mean "Always mourning, always Dowland." This is very appropriate as John Dowland was famous for being in a constant state of melancholy. This melancholic nature is very easy to hear in his music, particularly the Melancholy Galliard and the galliard If My Complaints.