  We investigated the electronic structures of the bandwidth-controlled
ruthenates, Y$_{2}$Ru$_{2}$O$_{7}$, CaRuO$_{3}$, SrRuO$_{3}$, and Bi$_{2}$Ru$%
_{2}$O$_{7}$, by optical conductivity analysis in a wide energy region of 5 meV
$\sim $ 12 eV. We could assign optical transitions from the systematic changes
of the spectra and by comparison with the O 1$s$ x-ray absorption data. We
estimated some physical parameters, such as the on-site Coulomb repulsion
energy and the crystal-field splitting energy. These parameters show that the
4$d$ orbitals should be more extended than 3$d$ ones. These results are also
discussed in terms of the Mott-Hubbard model.
