\subsubsection{The Musical Glass}

Before delving into the history of the singing wine glass per se, let's understand the singing/musical wine glass a little better. 

Essentially a singing wine glass (or armonica cup) is a glass bell. Like a conventional bell made of metal, it has a resonant frequency, and if energy is put into the bell somehow\EmDash{}by striking it, for example\EmDash{}it resonates at its resonant frequency. 

When you rub the rim of a wine glass with a wet finger, you're doing the same physics as a violin player sliding the bow over the string\EmDash{}the 'sticky' bow pulls the string to one side of the violin until it slips, and the bow is able to catch it and pull it again. This process repeats itself over and over hundreds if not thousands of times a second. The exact same process occurs when you rub your wet finger around the rim of the wine glass: your finger 'sticks' to the rim and torques the glass until it finally slips, until your finger is able to catch it and torque it again. This process repeats itself over and over (again, hundreds/thousands of times a second), which puts energy into the (glass) bell, whose physics only allow it to vibrate at musical frequencies. And, voil\`{a}! A musical sound!

The standard wine glass is ideal for this because the stem gives the player something to hold on to while their wet rubbing finger puts energy into the bowl: if the player holds the bowl itself, this prevents the sides from vibrating\EmDash{}and thus no musical sound.

Adding water lowers the pitch (which the reader can verify for themselves in their own kitchen) mostly because\EmDash{}in effect\EmDash{}it adds mass to the sides of the glass, effectively making the sides heavier and thus lowering the pitch of the glass.\footnote{The water also adds a compressive factor that additionally complicates matters. See \BrChanAOOJ{}. A similar phenomenon can be observed with bass piano strings, in which the steel wire is wrapped with copper wire to increase its mass without appreciably increasing its stiffness. }

% ??? FIGURE
 
Putting water inside the wine glass lowers the pitch, and so does putting water outside of the glass! Take a wine glass and check its pitch (with the wet finger around the rim); then run some water in your kitchen sink, put the glass in the sink so the glass is submerged except that the top part of the bell is above water, and check its pitch again. (See the figure below). Partially submerging the glass lowers the pitch.
 
In fact, having water both inside and outside of the glass lowers the pitch most of all. The reader can verify that adding water 'outside' the glass also lowers the pitch by placing a wine glass in a sink partially filled with water.

To recap: two essential elements are required for a musical glass: the walls of the bowl must be thin enough to vibrate easily, and it must have a stem\EmDash{}so the player can hold the glass by the stem without dampening the vibration of the bowl. You need both\EmDash{}thin-walled bowl, and a stem\EmDash{}or the wine glass simply will not sing with the wet finger around the rim.
Neither the Romans nor their Byzantine successors particularly cared about blowing thin glasses. But that was a hallmark of the Venetian glass blowers of the 14th through 16th centuries\EmDash{}particularly due to their invention of \textit{cristallo}. These glasses were available to the wealthy throughout Europe. 

