Possible Clues:

• The Party line - they can be beat - out of despondency
• Zero degrees latitude – where one is when low
• Belt of calms and light winds in the Atlantic and Pacific
• Musical instruments to entertain elderly in low spirits
• Former spirit's underlying Germany's stagnation
• Leaders of drinking society drink vintage liquor for melancholy
• Instruments curbing long-term depression
• Duke had mature spirits from equatorial region
• Period of depression — horse latitudes
• Daughter getting on alcohol's in depressed state