The two phenomena, the subjects of the present paper, have found a place in the current popular scientific literature of the day, and exercise a considerable influence on the opinions of the casual votaries of science, and even of some of those who are its regular cultivators. For that reason I shall go more into detail than otherwise would have been needed.

In the beginning of the session Professor Tait read a paper on Mirage, and exhibited to the Royal Society of Edinburgh an enlarged representation of an aërial phenomenon described by Professor Vince. The Professor of Mathematics inquired of me my opinion as to the explanation offered; and I now reply to Mr. Chrystal's inquiry indirectly, not by discussing in any way Mr. Tait's analysis, but by examining the major proposition, the reality of the phenomenon.