The popular belief that the moon's rays will cause madness in any person who sleeps exposed to them has long been felt to be absurd, and yet it has appeared to have its source in undoubted facts. Some deleterious influence is experienced by those who rashly court slumber in full moonshine, and probably there is no superstition to which the well-to-do pay more attention. Windows are often carefully covered to keep the moonbeams from entering sleeping rooms. A gentleman living in India furnishes "Nature" with an explanation of this phenomenon which is at least plausible. He says: "It has often been observed that when the moon is full, or near its full time, there are rarely any clouds about; and if there be clouds before the full moon rises, they are soon dissipated; and therefore a perfectly clear sky, with a bright full moon, is frequently observed. A clear sky admits of rapid radiation of heat from the surface of the earth, and any person exposed to such radiation is sure to be chilled by rapid loss of heat. There is reason to believe that, under the circumstances, paralysis of one side of the face is sometimes likely to occur from chill, as one side of the face is more likely to be exposed to rapid radiation, and consequent loss of its heat. This chill is more likely to occur when the sky is perfectly clear. I have often slept in the open in India on a clear summer night, when there was no moon; and although the first part of the night may have been hot, yet toward two or three o'clock in the morning, the chill has been so great that I have often been awakened by an ache in my forehead, which I as often have counteracted by wrapping a handkerchief round my head, and drawing the blanket over my face. As the chill is likely to be greatest on a very clear night, and the clearest nights are likely to be those on which there is a bright moonshine, it is very possible that neuralgia, paralysis, or other similar injury, caused by sleeping in the open, has been attributed to the moon, when the proximate cause may really have been the _chill_, and the moon only a remote cause acting by dissipating the clouds and haze (if it do so), and leaving a perfectly clear sky for the play of radiation into space." THE ARGUMENT AGAINST VACCINATION.