A narrow gap tested an unusual flow
Kapitsa’s 1938 report examined helium below the lambda transition, where flow through a narrow gap implied extraordinarily low viscosity. Allen and Misener independently reported related superfluid behavior.
The result depended on the flow geometry and on checking the character of the motion. An unusually large heat transport signal had motivated the investigation, but did not itself establish a viscosity value.
Different probes couple to different motion
A two-fluid description permits a normal component with entropy and viscosity alongside superfluid motion. An oscillating object can therefore experience damping even when a narrow-channel experiment is dominated by the superfluid component. The descriptions concern different responses of one liquid.
Low-temperature engineering sustained the physics
Kapitsa also developed methods for producing and handling low temperatures. Stable cooling and sensitive flow measurements made systematic studies possible. The 1978 award recognized his low-temperature inventions and discoveries, a scope broader than one viscosity measurement.
Sources: [3]
The source choice matters here
Kapitsa’s Nobel lecture discusses plasma and controlled fusion, so this helium article uses his original viscosity report and the official low-temperature award account. The linked pairing model supplies quantum-fluid context; it does not simulate the capillary apparatus.