The paper by F. Bloch discusses the phenomenon of nuclear induction, which occurs when a radiofrequency (RF) field is applied perpendicular to a constant magnetic field. This setup causes the nuclear polarization to precess around the constant field, leading to a component perpendicular to both fields. This component can induce observable voltages in a coil, providing a means to detect nuclear transitions without the need for molecular beams or complex detection methods. The author begins by explaining the principles of nuclear paramagnetism, where the magnetic moments of nuclei in a sample align with an external magnetic field, leading to a macroscopic polarization. The key assumption is that the changes in nuclear orientation are solely due to the external fields, with no significant influence from atomic moments or internuclear interactions. The main focus is on the behavior of the nuclear polarization under the influence of a strong constant field and a weak RF field. The polarization vector \( \mathbf{M} \) is shown to vary over time, and the induced voltage \( V \) is derived from this variation. The induced voltage reaches a maximum at resonance, proportional to the nuclear susceptibility \( \chi \), the strength of the magnetic field \( H \), and the frequency of the RF field \( \omega \). The paper also discusses the effects of thermal agitation and internuclear interactions on the polarization. These effects are described using relaxation times \( T_1 \) and \( T_2 \), which govern the rate of change of the polarization components. The relaxation times can significantly affect the observed induction effect, and the presence of paramagnetic catalysts can help reduce these effects. Finally, the author considers two limiting cases: "rapid passage" and "slow passage" through resonance. In the rapid passage case, the polarization is approximately constant near resonance, while in the slow passage case, all polarization components vanish at resonance. The induced voltage amplitude is derived for both cases, showing how it depends on the relaxation times and the variation of the external field. Overall, the paper provides a theoretical framework for understanding and detecting nuclear induction, highlighting its potential as a simple and effective method for observing nuclear transitions.The paper by F. Bloch discusses the phenomenon of nuclear induction, which occurs when a radiofrequency (RF) field is applied perpendicular to a constant magnetic field. This setup causes the nuclear polarization to precess around the constant field, leading to a component perpendicular to both fields. This component can induce observable voltages in a coil, providing a means to detect nuclear transitions without the need for molecular beams or complex detection methods. The author begins by explaining the principles of nuclear paramagnetism, where the magnetic moments of nuclei in a sample align with an external magnetic field, leading to a macroscopic polarization. The key assumption is that the changes in nuclear orientation are solely due to the external fields, with no significant influence from atomic moments or internuclear interactions. The main focus is on the behavior of the nuclear polarization under the influence of a strong constant field and a weak RF field. The polarization vector \( \mathbf{M} \) is shown to vary over time, and the induced voltage \( V \) is derived from this variation. The induced voltage reaches a maximum at resonance, proportional to the nuclear susceptibility \( \chi \), the strength of the magnetic field \( H \), and the frequency of the RF field \( \omega \). The paper also discusses the effects of thermal agitation and internuclear interactions on the polarization. These effects are described using relaxation times \( T_1 \) and \( T_2 \), which govern the rate of change of the polarization components. The relaxation times can significantly affect the observed induction effect, and the presence of paramagnetic catalysts can help reduce these effects. Finally, the author considers two limiting cases: "rapid passage" and "slow passage" through resonance. In the rapid passage case, the polarization is approximately constant near resonance, while in the slow passage case, all polarization components vanish at resonance. The induced voltage amplitude is derived for both cases, showing how it depends on the relaxation times and the variation of the external field. Overall, the paper provides a theoretical framework for understanding and detecting nuclear induction, highlighting its potential as a simple and effective method for observing nuclear transitions.