The absorption spectra of benzene derivatives in the vacuum ultra-violet. I

New photographs of the far ultra-violet spectrum of benzene are presented. The absorption from 2000 to 1800 A ($\lambda _{\max.}$, c. 1980 A) is regarded not as a part of the much stronger absorption of peak at 1790A but as due to a separate transition. Sharp bands lying at 1790A represent the first member of a previously reported Rydberg series. The spectra of toluene, xylene, monochloro- and o-dichlorobenzene, bromobenzene, iodobenzene and pyridine are briefly described, and the shifts relative to benzene are discussed. Two Rydberg series were observed for toluene, converging to a first ionization potential of 8$\cdot $77 $\pm $ 0$\cdot $05 V.