  We show that for any irrational number $\a$ and a sequence of integers
$\{m_l\}_{l\in \N}$ such that $\displaystyle{\lim_{l\to \infty} \norm{m_l \a} =
0}$, there exists a continuous measure $\mu$ on the circle such that
$\displaystyle{\lim_{l\to \infty} \int_\T \norm{m_l \th} d\mu(\th) = 0}$. This
implies that any rigidity sequence of any ergodic transformation is a rigidity
sequence for some weakly mixing dynamical system.
  On the other hand, we show that for any $\a \in \R - \Q$, there exists a
sequence of integers $\{m_l\}_{l\in \N}$ such that $\norm{m_l \a} \to 0$ and
$m_l \theta [1]$ is dense on the circle if and only if $\th \notin \Q \a+\Q$.

Dynamical Systems;Number Theory