CONTENTS[br] Introduction 658[br] I. Experimental Data on the Isotope Shift 659[br] 1. The Isotope Shift in the Spectra of Strontium, Zirconium, Molybdenum, and other Intermediate Elements 659[br] 2. The Isotope Shift in the Spectra of Isotopes of Heavy Elements of Neutron Numbers 82-126. 662[br] 3. The Isotope Shift in the Spectra of the Actinide Elements 666[br] II. Theory of the isotope Shift in the Spectra of the Heavy Elements 668[br] III. Comparison of the Theory of the Isotope Shift with Experiment 670[br] Bibliography 671[br]