  Our main object of study is a certain degree-one cohomology class of the
space K of long knots in R^3. We describe this class in terms of graphs and
configuration space integrals, showing the vanishing of some anomalous
obstructions. To show that this class is not zero, we integrate it over a cycle
studied by Gramain. As a corollary, we establish a relation between this class
and (R-valued) Casson's knot invariant. These are R-versions of the results
which were previously proved by Teiblyum, Turchin and Vassiliev over Z/2 in a
different way from ours.
