  During the low optical brightness states of AM Herculis systems (polars) when
accretion has declined to a very low value, the underlying magnetic white dwarf
photosphere can be modelled without the complication of thermal bremstrahlung
and cyclotron emission from the luminous accretion column. The far ultraviolet
spectra can be modelled with high gravity solar composition photospheres. In
this way, I present new temperatures and the first chemical abundance estimates
for the white dwarfs in three selected polars from the IUE NEWSIPS archive. For
the white dwarf in V834 Cen with Teff = 16,000$K, Si/H = 0.1 solar, C/H = 0.5
solar, for BY Cam, Teff = 17,000 K, Si/H = 0.1, C/H = 5 solar and for RX
J1313-32, Teff = 22,000 K, Si/H = 0.1 solar, C/H = 0.1 solar. The temperature
distribution of 24 white dwarfs in polars with known temperatures above and
below the period gap is compared with the distribution of the white dwarf
temperatures in dwarf novae during quiescence. In both cases, the magnetic
white dwarfs in polars are significantly cooler than the non-magnetics. For all
CV white dwarfs, magnetic and non-magnetic with Teff < 12,500 K, 91% of the
objects (10 out of 11) are magnetics in polars. This suggests that long term
accretion heating and cooling of white dwarfs in polars differs from the
effects of long term accretion in non-magnetic disk accretors.
