  We have measured the Balmer-series x-rays of kaonic $^4$He atoms using novel
large-area silicon drift x-ray detectors in order to study the low-energy
$\bar{K}$-nucleus strong interaction. The energy of the $3d \to 2p$ transition
was determined to be 6467 $\pm$ 3 (stat) $\pm$ 2 (syst) eV. The resulting
strong-interaction energy-level shift is in agreement with theoretical
calculations, thus eliminating a long-standing discrepancy between theory and
experiment.
