The paper by Bloembergen, Purcell, and Pound explores the relaxation effects in nuclear magnetic resonance (NMR) absorption. They investigate the exchange of energy between a system of nuclear spins in a strong magnetic field and the heat reservoir consisting of the lattice of the substance containing the magnetic nuclei. This exchange brings the spin system into equilibrium at a finite temperature, allowing it to absorb energy from an applied radiofrequency field. However, the absorption of energy tends to increase the spin temperature and decrease the absorption rate, leading to a "saturation" effect. This effect, along with the spin-lattice relaxation time \( T_1 \), can be measured. The interaction among magnetic nuclei, associated with a characteristic time \( T_2' \), contributes to the width of the absorption line. The authors describe the experimental setup, which involves a radiofrequency bridge to observe NMR absorption. They detail the method for deriving \( T_1 \) from saturation experiments and present results showing relaxation times ranging from \( 10^{-4} \) to \( 10^2 \) seconds. They also note that \( T_1 \) decreases with increasing viscosity in liquids, reaching a minimum before increasing again. The line width increases monotonically from a very small value to a value determined by the spin-spin interaction in the rigid lattice. The paper discusses the theoretical background, including the dynamics of spins in an oscillating field and the phenomenological theory of magnetic resonance absorption. They provide a detailed analysis of the saturation phenomenon and the measurement of relaxation times using both direct observation of recovery from saturation and the saturation-curve method. The saturation-curve method is applicable over a wider range but requires more complex analysis. The authors conclude with a discussion of the experimental limitations and the broad range of relaxation times observed in various substances.The paper by Bloembergen, Purcell, and Pound explores the relaxation effects in nuclear magnetic resonance (NMR) absorption. They investigate the exchange of energy between a system of nuclear spins in a strong magnetic field and the heat reservoir consisting of the lattice of the substance containing the magnetic nuclei. This exchange brings the spin system into equilibrium at a finite temperature, allowing it to absorb energy from an applied radiofrequency field. However, the absorption of energy tends to increase the spin temperature and decrease the absorption rate, leading to a "saturation" effect. This effect, along with the spin-lattice relaxation time \( T_1 \), can be measured. The interaction among magnetic nuclei, associated with a characteristic time \( T_2' \), contributes to the width of the absorption line. The authors describe the experimental setup, which involves a radiofrequency bridge to observe NMR absorption. They detail the method for deriving \( T_1 \) from saturation experiments and present results showing relaxation times ranging from \( 10^{-4} \) to \( 10^2 \) seconds. They also note that \( T_1 \) decreases with increasing viscosity in liquids, reaching a minimum before increasing again. The line width increases monotonically from a very small value to a value determined by the spin-spin interaction in the rigid lattice. The paper discusses the theoretical background, including the dynamics of spins in an oscillating field and the phenomenological theory of magnetic resonance absorption. They provide a detailed analysis of the saturation phenomenon and the measurement of relaxation times using both direct observation of recovery from saturation and the saturation-curve method. The saturation-curve method is applicable over a wider range but requires more complex analysis. The authors conclude with a discussion of the experimental limitations and the broad range of relaxation times observed in various substances.