The percentages are 1.5, 25.2 and 4.6.The data for the Clouds will change little with increase of numbers, and the ratio of 1 to 17, therefore, stands out as a most remarkable and suggestive phenomenon.4. That the period frequency anomaly is associated with the stage of development in these similar irregular galaxies is a fair supposition.The Small Cloud, on this hypothesis, is more "advanced" than the Large.It is intermediate in some of its evolutionary characteristics between the dust- and-gas rich Large Cloud and the dust-free Sculptor Cluster, which is a dwarf open-structure spheroidal galaxy very rich in variables of the cluster- type.4The Sculptor Cluster has few classical Cepheids and few highly luminous stars; the Small Magellanic Cloud has many of both, but the Large Cloud is much richer in such supergiants.The scores of Cepheids with periods around 1.5 days in the Small Cloud may be that system's version of cluster-type variation; and this observa- tion leads to the suggestion that the chemistry and the behavior of the Cepheids of a galaxy or globular cluster are related to its mass and stage of development.
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Conger et al. (1952) studied this question.