A 79-year record (1866-1944) of hourly surface pressure observations at Batavia (6.2¿S,106.8¿E) was analyzed to detect systematic long-period variations in the solar semidiurnal barometric oscillation (S2(p)). Evidence was found for a quasi-biennial oscillation (QBO) in S2(p) throughout the latter half of the record (1905-1944). This is attributed to the effect of the familiar QBO of the tropical stratospheric mean winds and temperatures on the solar semidiurnal tide. The results thus suggest that the stratospheric QBO itself has been proceeding in something like its present form since at least the beginning of the twentieth centruy. Some theoretical calculations were performed of the change expected in S2(p) between the minimum and maximum in the sunspot cycle by employing different published estimates of the solar ultraviolet flux variability. It is clear from the present S2(p) observations that, if there is any regular 11-year cycle in the solar ultraviolet flux at wavelengths >200 nm, then it must be much smaller than some of the published estimates based on direct flux measurements. However, for periods around two individual sunspot minima (1867 and 1913) there are changes in the Batavia S2(p) consistent with a large drop in solar ultraviolet output.