Page:Popular Science Monthly Volume 13.djvu/130

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THE POPULAR SCIENCE MONTHLY.

found in Northern Peru, the "rain-tree of Moyobamba," from the trunk of which, as the story runs, "water may frequently be seen to ooze, falling in rain from the branches in such quantity that the ground beneath is converted into a perfect swamp." The facts with regard to this "rain-tree" are stated as follows by Mr. Spence, the traveler, in a letter to Mr. Thiselton Dyer, which the latter has communicated to Nature. The tree is not a myth, but a fact, though the current story is not quite exact. Mr. Spence first witnessed the phenomenon in question in September, 1855. On a certain day, about seven o'clock in the morning, while in latitude 6° 30' south, longitude 76° 20' west, he found a "lowish, spreading tree, from which, with a perfectly clear sky overhead, a smart rain was falling. A glance upward showed a multitude of cicadas sucking the juices of the tender young branches and leaves, and squirting forth slender streams of limpid fluid." The tree belonged to the acacia tribe, but Mr. Spence was informed by his native attendants that almost any tree, when in a state to afford food to the nearly omnivorous cicada, might become, pro tempore, a Tamia-caspi, or raintree. Afterward, he himself verified this fact more than once. "As to the drip from the tree causing a little bog to form underneath and around it," writes Mr. Spence, "that is a very common circumstance in various parts of the Amazon Valley, in flats and hollows, wherever there is a thin covering of humus, or a non-absorbent subsoil, and the crown of foliage is so dense as to greatly impede evaporation beneath it."

 

Clearing Land with Dynamite.—A severe storm of wind having blown down a number of large trees on the estates of the Earl of Stamford and Warrington, recourse was had to the use of dynamite for the purpose of breaking up the roots, that being esteemed the most expeditious mode of removing those incumbrances. The first experiment was made on four very large elm-roots. An auger-hole, one and a half inch in diameter was bored in each, and charged with eight dynamite cartridges, which, on being exploded, shivered the roots into fragments suitable for firewood. The second experiment was on two huge oakroots. These were simply charged by placing a few cartridges of dynamite in natural crevices of the roots, without any auger hole. The charges were exploded, and the roots blown to pieces of manageable size. Next, an auger-hole was bored in each of seven oak-roots, and charged with two cartridges each, the result being that all were broken up. The fourth experiment was on an extraordinarily large ash-root, the great fangs of which were lying undisturbed in the ground. Underneath this a number of crowbar-holes were made and charged with dynamite. The fuses were all cut the same length and fired simultaneously, blowing the whole mass out of the ground.

 

Color-Blindness.—In an article on "Defective Vision considered in its Relations to Railroad Management," published in the Chicago Railway Review, Mr. Thomas F. Nelson, optician, remarks as follows on the phenomenon of color-blindness: "This defect but rarely assumes the form that would be termed absolute color-blindness, or want of any sensation of color. Where this form is perfectly developed there is generally a sharp, well-defined appreciation of differences between light and shade, or even between the finest grades of apparent brightness or intensity; but recognition of color is entirely wanting, there being no distinction whatever between different colors having the same degree of intensity. A curious fact might be noticed in this connection, that these defects are but rarely found in women.

"The more common form is that caused by the absence of perception of one of the three fundamental colors. These are mentioned in the order of their comparative frequency, viz., where the elementary sensation corresponding to red is wanting; next, the absence or imperfect perception of green, and third of blue. It will be noticed as a remarkable fact that the first two mentioned are now used to make up the entire code of railway-signals, and that this defect for red occurs more frequently than for any other color. This is an item of the greatest importance in railway and vessel management, since red is almost always used for the danger-signal. To add still fur-