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visible. To whatever we might attribute the light, it ought to be seen far better after the end of twilight in the evening than during the daytime. The fact that it is not seen then seems to be conclusive against its reality.

The appearance illustrates a well-known psychological law, that the imagination is apt to put in what it is accustomed to see, even when the object is not there. We are so accustomed to the appearance on the moon that when we look at Venus the similarity of the general phenomena leads us to make this supposed familiar addition to it.

During the past two centuries several observers have from time to time thought that they saw a satellite of Venus. Countless observers, with good telescopes, have seen nothing of the sort. We may safely say that Venus has no satellite visible in the most powerful telescopes of our time. Quite likely these supposed satellites were seeming objects quite familiar to astronomers under the name of "ghosts." These are sometimes seen when a telescope is pointed at a bright object, and are due to a double reflection of light in the lenses either of the object-glass or the eyepiece.

A few years ago the writer received a letter from the owner of a very large telescope in England stating that, by great care, he could see a very faint, round, and well-defined aureole of light around the planet Mars. He desired to know whether the object could be real, or how the appearance was to be explained. In reply, he was informed that such an appearance would be produced