  There are two de Rham complexes in diffeology. The original one is due to
Souriau and the other one is the singular de Rham complex defined by a
simplicial differential graded algebra. We compare the first de Rham cohomology
groups of the two complexes within the \v{C}ech--de Rham spectral sequence by
making use of the {\it factor map} which connects the two de Rham complexes. As
a consequence, it follows that the singular de Rham cohomology algebra of the
irrational torus $T_\theta$ is isomorphic to the tensor product of the original
de Rham cohomology and the exterior algebra generated by a non-trivial flow
bundle over $T_\theta$.
