Observations of the ß Cephei star 12 Lacertae have been made at both high time and spectral resolution with an Image Isocon television camera. The observations cover complete cycles of the pulsation on two consecutive nights in October 1972. The spectral region covered includes the two Si III inclines at λ 4553 and λ 4568. The line profile variations have been studied in detail; in particular the line doubling at certain phases of the pulsation. Wavelength shifts of the separate components were measured and a discontinuous radial velocity curve was obtained. / Science, Faculty of / Physics and Astronomy, Department of / Graduate