To be fair, the two instruments may resemble each other in appearance, but sound completely different, so a comparison between the two does not do either justice, the bagpipes have strong sound, and are mainly a instrument used in parades and marches (I think, correct me if I'm wrong), the uilleanns, like other instruments, are used in trad Irish and Irish Folk music. For the record, I am not a musician, but I have a 'good ear'.
Actually, they do not resemble each other very much at all, as this picture of the uillean pipes shows. They are, in a sense, the end product (thus far) of the two main branches of the bagpipe family -- there are literally dozens of different kinds of bagpipes, found from Ireland to Spain to Russia to India.
The uillean pipes (Gaelic for "elbow"; also called "union" pipes) are the best-known of the "cauld-wind" pipes (cold wind: powered by a bellows), as well as the latest, being about two centuries old. The next-best known are the Northumbrian pipes -- no awards for guessing where they're from. (I seem to recall cold-wind pipes are predominantly found in the British Isles.)
It's quite an art: you start by pumping the bellows with your right arm to keep the bag under your left arm inflated, but not overinflated, because your left arm is working to keep the pressure in the bag perfectly steady; variations in pressure can be heard as changes in pitch. And this is the easy part.
Next, of course, both hands are fingering the chanter (for the melody). But the chanter end can be placed against the leg (sometimes on a piece of leather, sometimes there's a valve on the end) to kick it into higher registers, so both hands, chanter and all are bouncing up and down. But even then you're not done.
Those pipes across the lap, they're not just drones; some at least are "regulators" (I'm a bit less certain of terminology here), which means they have keys that can be pressed by the outer edge of your right palm, so you can get different and very distinctive "drone chords" (my term).
The uillean pipes are used in traditional and folk music, and I like listening to them.
The Great Highland Bagpipe, the one everyone knows, is less advanced technically. It reached its current form (three drones) some 300-400 years ago and little has changed since then but substitution of materials. Goretex bags apparently now outnumber hide, the checkvalves in the blowsticks are probably *all* synthetic, plastic drone reeds are common (lacking the extreme heat&moisture sensitivity of Arundo Dornax cane reeds).
They are best known, are most often seen, marching in parades but their musical range and tradition goes far beyond that. There are, for example, the dance tunes: jigs, strathspeys and reels. There are the slow airs and laments. And these are just the ceol beag, the small or light music.
There is also a body of music known very little outside the piping community these days: < ahref= "http://www.piobaireachd.com/welcome.htm"> Piobaireachd (Pibroch), the classical solo music of the GHB. Most of this music is centuries old, and was often taught using not written staff notation but through canntaireachd, a very stylized form of chanting that conveys the notes and the specific ornamentation (runs of gracenotes) used. Piobaireachd, like everything else on the GHB, is always played entirely from memory -- and some pieces run to 40 minutes or more.
There are rules that help, I will admit. But it's still daunting to get up in front of a judge and play for even 10 to 15 minutes, knowing he has the score in front of him and will hear even an incorrect gracenote.
There are popular classics in this genre: Every piper hears the history of the most sinister Lasan Padruig Caogach, "A Flame of Wrath (for Squinting Peter)." I studied "The Desperate Battle (of the Birds)," which conveys the sense of birds chirping, then fighting. "The [captured] Piper's Warning to His [about to be ambushed] Master", because it breaks the rules of piobaireachd and he knew his chief would hear the errors. "Cha Till MacCrimmon" (there are various titles): a member of the great MacCrimmon piping family composed this on the eve of a battle of which he had premonition of his own death: "MacCrimmon, his hame, ne'er mair returnin'"
The greatest of the bagpipe laments belong to this genre. And then there are those whose titles just make one wonder (I don't know their history): The Big Spree, The Little Spree, the Injust Incarceration.
And then there is... "The Old Woman's Lullaby."
A lullaby... on the Great Highland Pipes.
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