  The axes of solar active regions are inclined relative to the east--west
direction, with the tilt angle tending to increase with latitude ("Joy's law").
Observational determinations of Joy's law have been based either on white-light
images of sunspot groups or on magnetograms, where the latter have the
advantage of measuring directly the physically relevant quantity (the
photospheric field), but the disadvantage of having been recorded routinely
only since the mid-1960s. White-light studies employing the historical Mount
Wilson (MW) database have yielded tilt angles that are smaller and that
increase less steeply with latitude than those obtained from magnetic data. We
confirm this effect by comparing sunspot-group tilt angles from the Debrecen
Photoheliographic Database with measurements made by Li and Ulrich using MW
magnetograms taken during cycles 21--23. Whether white-light or magnetic data
are employed, the median tilt angles significantly exceed the mean values, and
provide a better characterization of the observed distributions. The
discrepancy between the white-light and magnetic results is found to have two
main sources. First, a substantial fraction of the white-light "tilt angles"
refer to sunspots of the same polarity. Of greater physical significance is
that the magnetograph measurements include the contribution of plage areas,
which are invisible in white-light images but tend to have greater axial
inclinations than the adjacent sunspots. Given the large uncertainties inherent
in both the white-light and the magnetic measurements, it remains unclear
whether any systematic relationship exists between tilt angle and cycle
amplitude during cycles 16--23.
