Observation of {psi}(3770){yields}{gamma}{chi}{sub c1}{yields}{gamma}{gamma}J/{psi}

From e{sup +}e{sup -} collision data acquired with the CLEO detector at the Cornell Electron Storage Ring, we observe the non-DD decay {psi}(3770){yields}{gamma}{chi}{sub c1} with a statistical significance of 6.6 standard deviations, using the two-photon cascades to J/{psi} and J/{psi}{yields}l{sup +}l{sup -}. We determine {sigma}(e{sup +}e{sup -}{yields}{psi}(3770))xB({psi}(3770){yields}{gamma}{chi}{sub c1})=(18.0{+-}3.3= {+-}2.5) pb and branching fraction B({psi}(3770){yields}{gamma}{chi}{sub c1})=(2.8{+-}0.5{+-}0.4)x10{sup -3}. We set 90% C.L. upper limits for the transition to {chi}{sub c2} ({chi}{sub c0}): {sigma}xB