CORRESP ONDENCE. 



123 



SENSE OF DIRECTION IN ANTS. 

 Editor Popular Science Monthly : 



A short article on the " Sense of Direc- 

 tion 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 in- 

 sect by a very heavy load which it was car- 

 rying. When first noticed it was traveling 

 along a gravel walk in most approved fash- 

 ion, 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 pro- 

 ceeding 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 satisfac- 

 tory progress in this manner, the top of the 

 grass-blade seemed to furnish a convenient 

 point of observation, like a tree-top in a for- 

 est. 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 dis- 

 tance was greater than if measured in a 

 straight line, yet that the insect had act- 

 ually 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 short- 

 est way home." 



Edwin F. Lyford. 

 SpEnraFiELD, Mass., February 20, 1889. 



JAPANESE MAGIC MIRRORS. 

 Editor Popular Science Monthly : 



In the February number of the " Monthly," 

 in the " Miscellany," page 572, Prof. Menden- 

 hall's account of the Japanese " magic mir- 

 ror " is quoted. The reason which he gives 

 for the peculiar property that a few acci- 

 dentally 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 inter- 

 ested in the phenomenon, which has been 

 explained in many ways. By the process of 

 exclusion, all for the time being were dis- 

 carded but two. The first of these is given 

 by Prof. Mendenhall, viz., " When the mir- 

 ror is cast the cooling process has the effect 

 of drawing it slightly out of shape " ; and 

 the second endeavored to answer the ques- 

 tion by supposing that in the casting there 

 was produced a difference of density oppo- 

 site the ornamentations, which are in de- 

 cided 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 pol- 

 ish, it appeared quite evident that all " draw- 

 ing " and differences in density would be re- 

 duced 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 con- 

 dition, the casting is placed upon a solid 

 base, on which the figures in relief firmly 

 rest, leaving the intervening spaces practi- 

 cally 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 rub- 

 bing 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 di- 

 verging rays would enlarge the image, so as 

 to produce the fact of the phenomenon. 



G. 0. Rogers. 

 Apam, Mexico, February 1, 1889. 



SELF-POISONING BT SNAKES. 

 Editor Popular Science Monthly : 



In your January number you say, "To 

 what extent a poisonous serpent's bite is nox- 

 ious to itself is doubtful " ; and the testimo- 

 ny of Dr. Stradling there given tends to set- 

 tle the doubt in the negative. Bearing upon 

 this question is the following from Lieuten- 

 ant Michler's report to Major W. H. Emory, 

 United States Army, and bearing date July 

 29, 1856. It is to be found in Major Emo- 

 ry's report of the " United States and Mexi- 

 can 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 in- 

 fested 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 protuber- 

 ances 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 bedfel- 

 low you may have when you awake in the 



