Ask your friend whether he can decipher the following sign, which you pretend to have read over tne shop of an Armenian shoemaker . He will probably tell you that he is not conversant with Oriental languages. Tell him that the sign is written in good English and, while he smiles incredulously, lay a frameless mirror perpendicularly on the mysterious script, right across the quotation marks. The result is shown. We understand at once that the reflected image is the faithful copy of the written half, and we consequently believe that if we were allowed to see in a mirror our pencil, our hand, and the paper on which we write we would have no more trouble in writing and reading what we have written than if we were directly watching our pencil at work. This is too bold an Inference, and the following experiment shows how far it is from being true: Ask your friend to write anything he chooses, with the condition that he shall see his hand and read the script in the mirror only. With the help of a few books arrange the mirror and the paper as shown herewith. The writer sets at work, but will not probably go farther than the first letter. His hand seems to be struck with paralysis agitans, and unable to write anything but zigzags. You take his pencil and write rapidly and correctly in the same conditions. Your secret can be told in a few words: First, close your eyes; as long as you strive to follow the pencil in the mirror, your efforts to write are vain. Second, write in printed capitals and make no attempt to write anything but the pseudo Armenian sign and a few other sentences which participate of the same characteristic. What is that characteristic? It is not hard to find. Find it. The peculiar inversion of objects viewed in a mirror is of course the cause of the difficulty felt in reading or writing. The writer is left free to write froni left to right, but finds that while he is so doing, the mirror upsets his letters. There is an entirely distinct kind of inversion which can be best observed with the help of a mirror. The most suitable time for the making of the following experiment is after a meal the menu of which Included soft-boiled eggs. Take an egg shell and trim it with scissors so as to reduce it to a half shell. In the hollow bottom, roughly draw with your pencil a cross with pointed ends. Bore a hole, about the size of a pea, in the center of the cross. Place yourself so as to face a window, the light falling upon your face, not upon the mirror which you hold in one hand. Close one eye. Place the shell between the other eye and the mirror, at a distance of two or three Inches from either, the concavity facing the mirror. Through the hole in the shell look at the mirror as if this were some distant object. While you are so doing, the concave shell will suddenly assume a strongly convex appearance. You may then examine it directly in all its parts; no amount of auto-suggestion will allow Xou to get rid of the illusion. To destroy it, it becomes necessary either to open both eyes or to withdraw the shell away from the mirror. The nearer the shell to the mirror and the farther the eye from the shell the more readily comes the Illusion. The hole in the shell acts as a diaphragm, and its position, at some distance from the eye, favors the localization of the luminous pencils in the crystalline lens. Those which are emitted by the marginal parts of the egg are refracted exclusively by the marginal parts of the crystalline lens. They are more bent and give smaller images than the pencils which are sent by the center of the shell. The decreasing scale of reproduction from the center of the shell to its periphery offsets the influence of distance on the appearance of images of points situated on the anterior or posterior parts of the shell. In a recent issue of the Railroad Gazette Mr. A. Stuckl presented some very interesting data on the relative costs of steam and gas power, basing his estimates cn conditions obtaining in Pittsburg, and assuming a plant of 1,000 horse-power. He stated that the cost of 1,000 horse-power per year would be $13,125, a high-speed non-condensing engine being used, and $8,625 in the case of a triple-expansion condensing engine. The cost of the coal used was taken at $2.50 per ton. With natural gas at 15 cents per 1,000 cubic feet. 1,000 horse-power per year would cost $4,500, while if producer sas made from Pittsburg coal were used, the cost of the same amount of power would be 13,675.
This article was originally published with the title "Some Experiments with a Mirror" in Scientific American 97, 22, 398 (November 1907)