  Let $\theta $ be a Salem number and $P(x)$ a polynomial with integer
coefficients. It is well-known that the sequence $(\theta^n)$ modulo 1 is dense
but not uniformly distributed. In this article we discuss the sequence
$(P(\theta^n))$ modulo 1. Our first approach is computational and consists in
estimating the number of n so that the fractional part of $(P(\theta^n))$ falls
into a subinterval of the partition of $[0,1]$. If Salem number is of degree 4
we can obtain explicit density function of the sequence, using an algorithm
which is also given. Some examples confirm that these two approaches give the
same result.
