Understanding Harmonics—Part 2

How many pipers have a firm grasp of the physics of sound that causes the unique and rich sound of our bagpipes? We are told that we should maintain a pressure in the pipe bag that is at the chanter reed’s “sweet spot”, that pressure that causes the reed to maximally vibrate and bring out the most “harmonics” and richness of sound of the reed. But what, really, are harmonics?