This journal provides immediate access to some articles. Volume 28(4); April 1942 Astronomy The Calculation of Rotation Factors for Eclipsing Binary Systems PMCID: PMC1078433 Bacteriology The Identification and Characterization of Bacteriophages with the Electron Microscope PMCID: PMC1078431 Botany Concentration of Growth Hormone and Fruitfulness in the Montmorency Cherry PMCID: PMC1078432 Genetics An Autosomal Recessive Factor Inducing Semi-Sterility in Drosophila Melanogaster Females PMCID: PMC1078429 “Ataxia,” a Hereditary Nervous Disorder of the Rabbit PMCID: PMC1078430 Mathematics Certain Direct Products of the Groups of Self-Isometries PMCID: PMC1078434 Certain Congruence Criteria Connected with Fermat's Last Theorem PMCID: PMC1078435 Physics On the Physical Characteristics of the Hydra Cluster of Nebulae PMCID: PMC1078436 Journal Matter Original table of contents page Administrative content — journal masthead, notices, indexes, etc. | ||