soap film is entirely new. We hope that the observations which we have made on it will be of interest.
It is difficult to assign a reason why the addition of salt to the liquid should produce so great a change in the results. In part, the better conducting salt probably masks effects which when soap alone is used become predominant, but we think it likely that in part at all events it actually prevents the changes to which the change of conductivity is due.
However this may be, we venture to think that there can be no doubt as to the facts that whereas the conductivity of a thin unsalted soap film is considerably greater than that of the liquid in bulk, the difference is so reduced in the case of a salted film with or without the addition of glycerine that the mean thickness of a number of black films whether measured electrically or optically is the same to within the limits of the error of experiment.
