Things I learned were that the crystal (and steel) structure are important because every bit of compliance in the system absorbs energy and turns it into heat rather than reflecting it back into the structure. Bricks work too if they are hard fired.
Finding the exact resonant frequency can be difficult as it can change as the system begins to vibrate. Sometimes the harmonics are better than the fundamental frequency. If I were doing this today I'd probably clips a strain gauge to the material and use a feedback loop to localize to the peak energy absorption frequency.
That library has long been used for research and experiments involving resonance. The seismologists and structural engineers have had it full of instruments for 50 years and been studying how its resonances change periodically in response to weather and other natural cycles, and how they change permanently after earthquakes, and they have used shaking it to study wave propagation.
Apparently all you need is something that is big, resonates, and is coupled to the ground and you can do some fun science.
"Soil-Structure System Identification of Millikan Library North–South Response during Four Earthquakes (1970–2002): What Caused the Observed Wandering of the System Frequencies?" 
"The Millikan shaking experiments and high-frequency seismic wave propagation in Southern California" 
"Variations in the Natural Frequencies of Millikan Library Caused by Weather and Small Earthquakes" 
"Results of Millikan Library Forced Vibration Testing" 
"The Observed Wander of the Natural Frequencies in a Structure" 
This is sometimes needed next to old buildings where hammering will cause damage.
It has a section, where the frequency drops to subsonic at constant volume. So you can feel resonant frequencies.
This is kind of hard to do using just the visuals, as you run out of hands unless you play and fret the string with the same hand. But it works really nicely if you try to find the note by ear, and then use visual resonance as confirmation that you're right. Makes tuning pretty fun.
1) You're annoying the audience. Stop.
2) You're only tuning to yourself, not the band. Please use your tuning pedal.
If four instruments are following the standard and one is a bit flat because "A-440 Hz is arbitrary" then the whole band sounds like a mess.
In the case of guitar you only need a starting E tone and can figure out the rest by yourself.
In the case of an orchestra or concert band, everyone plays at once during tuning and you use the dissonance as a guide. Once there is no dissonance, everyone is in tune.
Be careful not to train your ears to hear the difference. Guitars playing chords are maddening collections of compromises and you will find yourself spiraling into sweetened tunings and fiddling with intonation instead of playing and enjoying music. Someday when you are adjusting your microtonal frets between songs, remember I warned you.
I think this would work only if the system in question is reasonably linear though, which wine glass might not be (?)
I can already do that, but it’s not a good habit.
Being able to get things done is a good habit.
There's of course a balance somewhere in the middle, but doing 50 projects in 50 days and having to work quick and write code that "works" is certainly a valuable skill.
aubio notes -r $(aubio pitch myfile.wav)
I love why the lucky stiff's writing, I love POODR (http://www.poodr.com/) and the two languages have a lot in common if you just keep an open mind about it :)
>> I do appreciate the effort you've put into this response, unlike parent. Well done
I'm happy you provided me with standard HN comments, though. Well done, to you, too. Very VIP HN.