Page:Popular Science Monthly Volume 35.djvu/135

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Editor Popular Science Monthly:

A short article on the "Sense of Direction in Insects," in the February number of "The Popular Science Monthly," served to remind me of an account of the travels of an ant told me by my father, the late Prof. Lyford. His attention was drawn to the insect by a very heavy load which it was carrying. When first noticed it was traveling along a gravel walk in most approved fashion, and, while occasionally avoiding a large pebble, was pursuing in the main a very straight line. But soon it turned from the walk, and taking a different direction entered a grass-plat. Here a different mode of proceeding was adopted. Finding it difficult to walk around the grass-stalks, it would climb to the top of the blade, let it bend down with its weight, then get off and climb a second, and so on. Besides making quite satisfactory progress in this manner, the top of the grass-blade seemed to furnish a convenient point of observation, like a tree-top in a forest. Through the grass the route was very direct until it reached its "hill," when it disappeared. A careful calculation of the distances traveled on the gravel and through the grass, and of its rate of progress over the two, indicated that, while the total distance was greater than if measured in a straight line, yet that the insect had actually selected, very nearly if not exactly, the route which could be traversed in the shortest time, seeming to realize that in this case at least "the longest way round was the shortest way home."

Edwin F, Lyford.
Springfield, Mass., February 20, 1889.



Editor Popular Science Monthly:

In the February number of the "Monthly," in the "Miscellany," page 572, Prof. Mendenhall's account of the Japanese "magic mirror" is quoted. The reason which he gives for the peculiar property that a few accidentally possess of reflecting upon a screen an enlarged image of the figures in relief on the back of the mirror seems to me, to say the least, questionable.

While in Japan I became intensely interested in the phenomenon, which has been explained in many ways. By the process of exclusion, all for the time being were discarded but two. The first of these is given by Prof. Mendenhall, viz., "When the mirror is cast the cooling process has the effect of drawing it slightly out of shape"; and the second endeavored to answer the question by supposing that in the casting there was produced a difference of density opposite the ornamentations, which are in decided relief. It was argued that the more dense portions would be abraded less in the operations of grinding and polishing than the softer parts, hence leaving them a very little in relief. There is no design, in the mind of the artist, for an unequal density in the casting, and, so far as I am aware, there is no proof that it exists. In observing the mode of grinding the face for the final polish, it appeared quite evident that all "drawing" and differences in density would be reduced to quite the same level. The process of final finish seemed to me to solve the puzzling riddle, which is as follows: When the moderately convex surface has been brought to a satisfactory and equable condition, the casting is placed upon a solid base, on which the figures in relief firmly rest, leaving the intervening spaces practically unsupported. In order to get all the "drawing" and unevenness out of the face of the casting, some are ground thinner than others. The final polish is given by violently rubbing the surface with the rather small end of a soft-wood stick, applied with heavy pressure. It seems evident that when the stick passes from the thick supported to the thin unsupported parts, the latter would be slightly depressed, and the continued rubbing pressure would fix these depressions, leaving slightly raised lines exactly opposite the ornamentations in relief on the back. These are so slight as not to be detected by the eye, but when cast from the convex surface on a screen at some distance the diverging rays would enlarge the image, so as to produce the fact of the phenomenon.

G. O. Rogers.
Apam, Mexico, February 1, 1889.



Editor Popular Science Monthly:

In your January number' you say, "To what extent a poisonous serpent's bite is noxious to itself is doubtful"; and the testimony of Dr. Stradling there given tends to settle the doubt in the negative. Bearing upon this question is the following from Lieutenant Michler's report to Major W. H. Emory, United States Army, and bearing date July 29, 1856. It is to be found in Major Emory's report of the "United States and Mexican Boundary Survey," vol. i, pp. 121, 122.

"The glare of our fires attracted a large number of rattlesnakes; the whole place "(the "Sierra del Poso Verde")" seemed infested with them. We judged them to be a new species from their tiger-colored skins; they were exceedingly fierce and venomous. On the deserts of the Colorado we had often seen others with horns, or small protuberances above the eyes; and Dr. Abbott has taken from the body of still another species quite a number of small ones, among which was a monstrosity with two perfectly formed heads attached to one neck. When you lie down on your blankets stretched on the ground, you know not what strange bedfellow you may have when you awake in the