Page:Popular Science Monthly Volume 50.djvu/710

690 other substances to harden it or diminish the price. Caoutchouc gutteux is sometimes added to make it more supple, and a certain degree of elasticity may be imparted to it by adding India rubber of good quality. With the perfect machinery now employed it is made into sheets of almost any desired thickness. Many articles are molded and the seams are finished with a hot iron. Cords and tubes are made by a machine employed for similar articles in the manufacture of India rubber, and which is on the principle of one used in making macaroni. Belting is made for use in moist air or where acid vapors are given off. Such belts have less resistance than those made of rubber or leather, and are only used for small powers. According to Meyer's Lexikon, there is a transparent gutta-percha varnish which can be used for covering documents. It does not change the paper; the document is perfectly protected against water, acids, and alkalies; and the writing can not be erased. Gutta-percha is also used in dentistry.

At the International Congress of Electricity at Paris, in 1881, the alarm was sounded in regard to the decreasing supply of this substance, and England, France, and Holland caused investigations to be made with a view to gutta-percha planting, but they do not seem to have led, as yet, to any specially practical results. Land of volcanic origin has been observed to be favorable, and heat and light and constant humidity the conditions essential for the growth of the tree. There are vast regions in Cochin China and Cambodia where, it is said, the Isonandra could be grown at slight expense; while all Malaysia, and probably other regions where it grows native, would be found to lend themselves to the same purpose. As the tree requires thirty years to reach maturity, little can be expected from private enterprise, and national aid should be extended. Meanwhile, the increasing demands of submarine telegraphy, etc., and the ruthlessness of gatherers are making it scarcer, and manufacturers must speculate with very variable prices.

his presidential address before the Royal Geographical Society Sir Clements R. Markham cites the execution of the Periyar Canal, in the Madras Presidency, India, as a most striking example of the power of man to alter permanently the physical geography of a region. The Periyar flows northward between the ridges of the western Ghauts Mountains, breaks through them, and reaches the coast on the western side, in a region abundantly supplied with water, while Madura, on the east side, is an arid plain, constantly parched. The canal has been completed, with a tunnel through the mountains, and the river has been turned to the western side, making the effectual irrigation of Madura practicable. As opposed to the too many instances in which man has injured the countries some of whose geographical conditions he has changed, we have one here in which by careful calculations and high engineering skill he has conferred great and lasting benefit upon a region.