Observation of $\Upsilon(1S) \to \gamma K_S K_S$

Using data collected by the CLEO III detector at the Cornell Electron Storage Ring (CESR), we report on the observation of the radiative decay of $\Upsilon(1S)$ to $K_S K_S$ via production of $f_2'(1525)$. The $\Upsilon(1S)\rightarrow\gamma f_2'(1525)$ branching ratio obtained is consistent with previous measurements.