TRICKS OF VISION | AdventAI

International Tract and Missionary Society · Oakland, California · Mar 10, 1887

FromSigns of the Times, Vol. 13, No. 10.

TRICKS OF VISION.

M. EMIL SOREL, in La Nature, says: "There are days on which, in certain weather, and despite the curvature of the earth, the distance of visibility is doubled or more than doubled. This phenomenon is explained to us by a well-known law of physics. If we throw a coin into an empty vessel, it will be hidden by the edge of the latter, at a certain distance; but if we fill the vessel with water, the coin will become visible. We have here a case of refraction, such as is explained in elementary works on physics.

"Every one also knows the theory of the mirage put forth by the celebrated Monge, who explains the phenomenon as due to a diminution of the air's density in contact with the superheated earth. A contrary theory will explain the mirage at sea. While the sun is making the atmosphere intensely hot, the sea and the strata of air in contact therewith remain relatively cold, and these strata become superposed in the order of their density. A luminous ray emanating from the sea will pass from one stratum into another of less density, there will be a refraction, and an object beneath the horizon will be seen above it.

"This theory supposes two conditions, to wit, a heating of the atmosphere, while the

sea and the earth remain relatively cold, and a calmness of it to permit its strata to become superposed in the order of their density. It is precisely when these two conditions are fulfilled that the phenomenon of the mirage occurs. On such days ships rise instead of descending in measure as they recede. As the horizon is perceived by direct visibility, a ship is finally seen above the horizon as if it were suspended in the air. It is the famous "phantom ship," familiar to sailors—a visible ship in the natural, upright position. If atmospheric conditions were favorable, a second ship would be seen above the first, etc. Certain mariners worthy of credence have assured me that they have seen as many as seven superposed ships."