  The spontaneous motion of a camphor particle with a slight modification from
a circle is investigated. The effect of the shape on the motion is examined by
the perturbation method. We introduce a slight $n$-mode modification from a
circle, where the profile is described by $r = R(1 + \epsilon \cos n\theta)$ in
polar coordinates. The results predict that a camphor particle with an $n=3$
mode modification from a circle, i.e., a triangular modification, moves in the
direction of a corner for a small particle, while it moves in the direction of
a side for a large particle. The numerical simulation results well reproduce
the theoretical prediction. The present study will help understand the effect
of the particle shape on spontaneous motion.
