@inproceedings{g.1936on,
title={On invariant and semi-invariant aberrations of the symmetrical optical system},
author={G. C. Steward},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203109140138563},
booktitle={Acta Mathematica},
volume={67},
number={1},
pages={213-250},
year={1936},
}
G. C. Steward. On invariant and semi-invariant aberrations of the symmetrical optical system. 1936. Vol. 67. In Acta Mathematica. pp.213-250. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203109140138563.