The reason for this uncertainty is that the physical conditions in the sphere where lightning occurs, according to other experiences of electric phenomena, actually exclude the formation of such high tensions as are necessary for the occurrence of discharges on the scale of lightning. If we look at this fact without scientific bias we are once again reminded of the Hans Andersen child. We cannot help wondering how this child would behave in a physics class if the teacher, after vainly trying to produce a lightning-flash in miniature with the help of an electrical machine, explained that the moisture prevalent in the air was responsible for the failure of the experiment, and that he would have to postpone it to a day when the air was drier. It would scarcely escape the Hans Andersen child that the conditions announced by the teacher as unfavourable to the production of an electric spark by the machine, prevail in a much higher degree exactly where lightning, as a supposed electric spark, actually does occur.