  We have analysed the three-colour photometry of 34 pulsating red giants that
was published by Percy, Wilson and Henry (2001). As is common with
semiregulars, many of these stars have long secondary periods (LSPs) of several
years, in addition to the usual shorter-period pulsations. We measured
pulsation amplitudes in VRI and found that both the V/R and V/I amplitude
ratios in most stars are systematically lower for the LSPs that for the shorter
periods. These results must be taken into account by any theory that attempts
to explain LSPs.
