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The magnetization curves of tin and mercury cylinders were measured in transverse magnetic fields at a variety of temperatures in the superconducting range, and for various cylinder radii from 1.8 x 10 -2 to 1.7 X 10 -3 cm. As the cylinder radius was reduced the magnetization curve departed more and more from the simple form to be expected for an infinite cylinder of large radius, and the details of the departures agree qualitatively with the predictions of Landau’s theory of the intermediate state. The experiments show also that the sharp drop of magnetization corresponding to entry into the intermediate state coincides closely with the appearance of resistance. Detailed comparison with Landau’s theory (as worked out more fully by Andrew in part III) yields estimates of the surface energy at a boundary between normal and superconducting phases at the various temperatures.

has reported the occurrence of superconductivity in quickly frozen solutions of sodium in ammonia. In view of the fact that all other superconductors have transition points of the order of 5°K, corresponding to an excitation energy of 5X10~4 ev, the appearance of superconductivity at very much higher temperatures (about 200°K) is somewhat unexpected.We have repeated Ogg's conductivity experiment on a number of concentrations ranging from 0.7N to 2N and noted in agreement with his work that the resistance drops very appreciably on freezing. However by making a current and potential measurement we found that the small residual resistance was caused by the solution itself, and not as Ogg suggests by a contact resistance at the electrodes.It might be mentioned that Ogg's interpretation of the observed magnetic moment in a ring is not necessarily as conclusive as may appear at first sight. If a ring is frozen in a magnetic field and the field subsequently switched off, a magnetic moment due to paramagnetic regions within the material which have lost their ability to reorientate themselves could be mistaken for a persistent current. A more conclusive test is to freeze a ring in zero magnetic field and to attempt to induce a current by switching on and off a strong magnetic field. However, in a considerable niimber of experiments on rings with the concentration range stated above, we were unable to observe a residual magnetic moment with either technique of inducing a persistent current. Richard A. Ogg, Phys. Rev. 69, 243 and 544 (1946 I N a recent Letter to the Editor on the above subject, K. Sun 1 has pointed out that if Bethe's 2 calculation of the mass of the neutron is repeated, using Mattauch's 3 more recent values for the H^-D mass difference and the H 1 mass, a slightly lower neutron mass results. The value he obtains is 1.008 92 db0.000 04 as compared to Bethe's 1.008 93=b0.000 05. In the calculation, however, Sun used the same value as Bethe for the deuteron binding energy, namely 2.17±0.04 Mev, the uncertainty in this quantity being the main source of uncertainty in the neutron mass.The binding energy of the deuteron is now known more accurately than the above figure indicates and the more recent results should be used in the calculation. Wiedenbeck and Marhoefer 4 give 2.185 ±0.006 Mev for the deuteron binding energy. This latter value, together with Mattauch's 0.001 539 ±0.000 0021 mass unit for the H2 X -D difference, give the neutron-proton mass difference directly as 0.000 807±0.000 0068 or 751 ±6.3 Kev. Using the H 1 mass of Mattauch (1.008 130±0.000 0033), we then get a neutron mass of 1.008 93 7 ±0.000 0075. Thus the final mass, instead of being about 9 Kev lower than Bethe's value, and with an uncertainty of 37 Kev, is 6.5 Kev higher, with an uncertainty of only 7 Kev. i K. Sun, Phys. Rev. 69, 240 (1946). 2 H. Bethe, Phys. Rev. 53, 314 (1938). s J. Mattauch, Phys. Rev. 57, 1155 (1940).

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