  Variations in the propagation of globally-propagating disturbances (commonly
called "EIT waves") through the low solar corona offer a unique opportunity to
probe the plasma parameters of the solar atmosphere. Here, high-cadence
observations of two "EIT wave" events taken using the Atmospheric Imaging
Assembly (AIA) instrument onboard the Solar Dynamics Observatory (SDO) are
combined with spectroscopic measurements from the Extreme ultraviolet Imaging
Spectrometer (EIS) onboard the Hinode spacecraft and used to examine the
variability of the quiet coronal magnetic-field strength. The combination of
pulse kinematics from SDO/AIA and plasma density from Hinode/EIS is used to
show that the magnetic-field strength is in the range ~2-6 G in the quiet
corona. The magnetic-field estimates are then used to determine the height of
the pulse, allowing a direct comparison with theoretical values obtained from
magnetic-field measurements from the Helioseismic and Magnetic Imager (HMI)
onboard SDO using PFSS and local-domain extrapolations. While local-scale
extrapolations predict heights inconsistent with prior measurements, the
agreement between observations and the PFSS model indicates that "EIT waves"
are a global phenomenon influenced by global-scale magnetic field.
