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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 travel- 

 er, 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 suck- 

 ing 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 in- 

 formed by his native attendants that al- 

 most any tree, when in a state to afford food 

 to the nearly omnivorous cicada, might be- 

 come, pro tempore, a Tamia-caspi, or rain- 

 tree. Afterward, he himself verified this 

 fact more than once. "As to the drip from 

 the tree causing a little bog to form under- 

 neath and around it," writes Mr. Spence, 

 " that is a very common circumstance in vari- 

 ous 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 great- 

 ly impede evaporation beneath it." 



Clearing Land with Dynamite. A se- 

 vere 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 be- 

 ing 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 oak- 



roots. These were simply charged by plac- 

 ing a few cartridges of dynamite in natu- 

 ral 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 un- 

 disturbed 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 simulta- 

 neously, blowing the whole mass out of the 

 ground. 



Color-Blindness. In an article on " De- 

 fective 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 de- 

 fect 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 gener- 

 ally a sharp, well-defined appreciation of 

 differences between light and shade, or even 

 between the finest grades of apparent bright- 

 ness or intensity ; but recognition of color 

 is entirely wanting, there being no distinc- 

 tion whatever between different colors hav- 

 ing the same degree of intensity. A curi- 

 ous 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 men- 

 tioned in the order of their comparative 

 frequency, viz., where the elementary sen- 

 sation corresponding to red is wanting; 

 next, the absence or imperfect perception 

 of green, and third of blue. It will be no- 

 ticed 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- 



