  A histogram display of the solar neutrino capture-rate measurements made by
the GALLEX experiment appears to be bimodal, but that of the follow-on GNO
experiment does not. To assess the significance of these results, we introduce
a "bimodality index" based on the probability-transform procedure. This
confirms that the GALLEX measurements are indeed bimodal (at the 99.98 percent
confidence level), and that the GNO measurements are not. Tracking the
bimodality index as a function of time shows that the strongest contribution to
bimodality comes from runs 42 to 62, i.e. from the time interval 1995.1 to
1996.9. The bimodality index for the first half (runs 1 through 33) is 2.56,
whereas that for the second half (runs 33 through 65) is 7.05. Power-spectrum
analysis shows a similar distinction: the peaks in the power spectrum formed
from the second half are stronger than those in the power spectrum formed from
the first half, suggesting that bimodality and rotational modulation are
related.
