A short monograph detailing the scientific* work on human auras. Published in 1949 with several reprints (the one I read was from 1968). There's historical sections detailing the work of Anton Mesmer & co., a practical guide to analyzing the colors of different auras, and a useful how-to guide for people interested in developing the skill of viewing auras.
There's a section detailing the division of the aura into three interlocking sections: the Etheric, Astral, and Mental "bodies." In this field of interest, these terms are often used interchangeably, and it was interesting to see a specific breakdown like this.
This is a quick and worthwhile read if you're interested in the topic (either from a practical or academic standpoint).
* Then, as now, this wording is grounds for argument.