In 1925, the earliest spectral analysis of the component stars was achieved by Robert Julius Trumpler (1886-1956) in his classic paper "Spectral Types in Open Clusters". It is likely that this work inspired another close inspection of the Jewel Box, and this continued with numerous publications, at least until the culmination of the classic book, Harlow Shapley's "Star Clusters.". Harvard Observatory's Monograph No. 2 (1930). It was Shapley and Melotte who classed the Jewel Box as Type 'g' -considerably rich and concentrated. In 1929, Trumpler used thirty stars within the inner 6' radius and gave NGC 4755 the more modern 'I 3 r -' classification, which first appeared in "Preliminary Results on the Distance, Dimensions, and Space Distribution of Open Star Clusters", Lick Obs. Bull., 14, 154 (1930). The 'I 3 r -' stating:
“Detached, strong concentration, bright and faint stars in the cluster, rich in stars, without nebulosity”.
As the original data on the southern cluster was so scant, it was eventually Ruprecht who confirmed this initial classification (Bull. Astron. Inst. Czech., 17, 34 (1966)).
“Southern Astronomical Delights” © Andrew James (2002) Sydney, Australia