## Abstract

The resistance of tin and mercury cylinders was measured in transverse magnetic fields between 1$\cdot $5 degrees K and the superconductivity transition temperature, for cylinder radii from 5 $\times $ 10$^{-2}$ cm. to 1$\cdot $3 $\times $ 10$^{-3}$ cm. It was found that the field $\rho $H$_{c}$, which first caused the appearance of resistance, and which is well known to be greater than $\frac{1}{2}$H$_{c}$, increased with decreasing radius approximately in the manner predicted by Landau's theory of the intermediate state. There have been considerable discrepancies between the results of previous workers concerning the temperature dependence of $\rho $, and on the basis of the present measurements it has been possible to suggest plausible explanations of the discrepancies. It has been shown that the resistance and magnetic induction in the intermediate state are closely correlated as might be expected. Using this correlation in conjunction with the magnetic behaviour predicted on the basis of Landau's theory (see following paper referred to as III), estimates are obtained of the surface energy at the boundary between superconducting and normal phases; it is the finite size of this energy which is responsible for the fact that $\rho $ is greater than $\frac{1}{2}$.