690 POPULAR SCIENCE MONTHLY. 



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 resist- 

 ance than those made of rubber or leather, and are only used for 

 small powers. According to Meyer's Lexikon, there is a trans- 

 parent gutta-percha varnish which can be used for covering 

 documents. It does not change the paper ; the document is per- 

 fectly protected against water, acids, and alkalies ; and the writ- 

 ing 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 investiga- 

 tions 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 matu- 

 rity, little can be expected from private enterprise, and national aid 

 should be extended. Meanwhile, the increasing demands of sub- 

 marine telegraphy, etc., and the ruthlessness of gatherers are mak- 

 ing it scarcer, and manufacturers must speculate with very variable 

 prices. 



In 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 opposetl to the 

 too many instances in which man has injured the countries some of who? e 

 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. 



