Following the papers on instability in binary systems, Dr S. Gaposchkin described a classification scheme that he had devised to describe the eclipsing binaries having emission lines, gas streams, or thick atmospheres. Such stars Gaposchkin calls the ‘camouflaged eclipsing variables’, and divides them into five groups:

1. (1) Typical members are UX Mon and SX Cas: the spectral type of the brighter star is B or A, that of the fainter is G or later. The minima are of equal depth. Balmer emission is present.

2. (2) Prototypes are β Lyr and ν Sgr: only one component can be seen distinctly, but two minima are present in the light curve. The spectroscopic behaviour is most complicated.

3. (3) Prototypes are RT And and YY Gem: the spectral class is G or later. Ca 11 emission is present. The depths of the minima are roughly equal, and the dimensions of the components are about the same.

4. (4) The prototype is DN Ori: both components are so well camouflaged that no definite velocity variation has been observed.

5. (5) Prototypes are V444 Cyg or UX UMa: the bright lines are strong, and their displacements and intensities do not vary in a simple manner with phase.