BEER MUSIC ANSWER

The note produced when you blow across the neck of a bottle is caused by the vibration of the air in the bottle, just like in any wind instrument.  The wavelength of the note produced is defined by the length of the air column in the bottle.  More precisely, if the bottle were idealised as a cylinder with one closed end and one open end, then one would expect one quarter of a wavelength to fit in the bottle with a "node" at the closed end and an "antinode" at the open end (actually slightly less because of something called the "end correction", but we will ignore that here).  So, if we multiply the length of the bottle, we get the wavelength of the sound produced.  The bottle with least water in it has the longest air column, therefore produces the longest wavelength note, i.e. the lowest pitch note.  The bottle with the least water has the shortest air column, therefore produces the shortest wavelength note, i.e. the highest pitched note.  

So, now for some mathematics!  If a beer bottle stands about 20cm high, then we would expect the wavelength of the sound to be about 80cm (0.8m) long.  This can be converted into frequency by using the formula:

wave velocity = frequency x wavelength

so, frequency = wave velocity / wavelength

and sound is known to travel at about 340 metres per second in air, so

frequency = 340 / 0.8 = 425Hz

Next, a quick trip to the tuning fork in my violin case tells me that the note "A"  has a frequency of 440Hz.  So, A flat must be a slightly lower frequency than that (in fact it is 415.3Hz at concert pitch), so this simple calculation has shown A flat to be a perfectly reasonable note to expect.  In fact, my beer bottles were slightly taller than 20cm, hence the small amount of water in the first one to reduce the height sufficiently to hit A flat.

A flat minor would require a small amount of water to be tipped out of the second bottle from the left, in order to flatten the note C to C flat and therefore create the minor third. Alternatively, of course, one could just drop a piano down a mine shaft....