  We present a photometric study of I-band variability in the young cluster IC
348. The main purpose of the study was to identify periodic stars. In all we
find 50 periodic stars, of which 32 were previously unknown. For the first time
in IC 348, we discover periods in significant numbers of lower-mass stars (M <
0.25 Msun) and classical T-Tauri stars. This increased sensitivity to
periodicities is due to the enhanced depth and temporal density of our
observations, compared with previous studies. The period distribution is at
first glance similar to that seen in the Orion Nebula Cluster, with the
higher-mass stars (M > 0.25 Msun) showing a bi-modal period distribution
concentrated around periods of 2 and 8 days, and the lower-mass stars showing a
uni-modal distribution, heavily biassed towards fast rotators. Closer
inspection of the period distribution shows that the higher mass stars show a
significant dearth of fast rotators, compared to the Orion Nebula Cluster,
whilst the low mass stars are rotating significantly faster than those in
Orion. We find no correlation between rotation period and K-L colour or H-alpha
equivalent width.
  We also present a discussion of our own IC 348 data in the context of
previously published period distributions for the Orion Nebula Cluster, the
Orion Flanking Fields and NGC 2264. We find that the previously claimed
correlation between infrared excess and rotation period in the ONC might in
fact result from a correlation between infrared excess and mass. We also find a
marked difference in period distributions between NGC 2264 and IC 348, which
presents a serious challenge to the disc locking paradigm, given the similarity
in ages and disc fractions between the two clusters.
