计算下列极限.
(1) $\lim \limits_ {x \rightarrow 0}( \cos x x^{2})^{ \dfrac {1}{x \ln (1 x)}}$.
(2) $\lim \limits_ {x \rightarrow 0}(e^{x} e^{ \sin 2x}-1)^{ \frac {1}{x}}$.
(3) $\lim \limits_ {x \rightarrow \infty } \left ( \dfrac {x-1}{x 1} \right )^{2x}$.
(4) $\lim \limits_ {x \rightarrow 0} \left ( \dfrac { \arctan x}{x} \right )^{ \dfrac {1}{x^{2}}}$.