  NGC288 is a globular cluster with a well-developed blue horizontal branch
covering the u-jump that indicates the onset of diffusion. It is therefore well
suited to study the effects of diffusion in blue horizontal branch (HB) stars.
We compare observed abundances with predictions from stellar evolution models
calculated with diffusion and from stratified atmospheric models. We verify the
effect of using stratified model spectra to derive atmospheric parameters. In
addition, we investigate the nature of the overluminous blue HB stars around
the u-jump. We defined a new photometric index sz from uvby measurements that
is gravity-sensitive between 8000K and 12000K. Using medium-resolution spectra
and Stroemgren photometry, we determined atmospheric parameters (T_eff, log g)
and abundances for the blue HB stars. We used both homogeneous and stratified
model spectra for our spectroscopic analyses. The atmospheric parameters and
masses of the hot HB stars in NGC288 show a behaviour seen also in other
clusters for temperatures between 9000K and 14000K. Outside this temperature
range, however, they instead follow the results found for such stars in omega
Cen. The abundances derived from our observations are for most elements (except
He and P) within the abundance range expected from evolutionary models that
include the effects of atomic diffusion and assume a surface mixed mass of
10^-7 M0. The abundances predicted by stratified model atmospheres are
generally significantly more extreme than observed, except for Mg. When
effective temperatures, surface gravities, and masses are determined with
stratified model spectra, the hotter stars agree better with canonical
evolutionary predictions. Our results show definite promise towards solving the
long-standing problem of surface gravity and mass discrepancies for hot HB
stars, but much work is still needed to arrive at a self-consistent solution.
