In October, 1873, Bell began experiments at 292 Essex Street in Boston using vibrating reeds (R) set in motion by speaking into the mouthpiece or orifice (O). A platinum wire (P) attached to the reed (R) dipped into a cup of liquid -- in this case, mercury (M). the round mouthpiece that Bell spoke into was made of gutta percha (gg). The drawing is in the Library of Congress.