228 IVORY AND THE P^LEPHANT 



The tensile strength is so great that thin longitudinal strips 

 cut from a whole tusk have constituted excellent riding 

 whips. 



Ivory is electrically positive and in the electrostatic series 

 of Faraday occupies a place between cat fur and bear fur 

 on the one hand and feathers and quartz on the other.* 

 Its relative radiating and reflecting power as compared 

 with some other substances is given as follows if 



RADIATING AND REFLECTING 



ABSORBING POWER POWER 



Lamp black 100 



Water 100 



Carbonate of lead 100 



Ivory, jet, marble 93-98 7-2 



Glass 90 10 



Ice 85 15 



Special tests of the tensile and compressive resistance, 

 and of the elastic properties of ivory were made for this 

 work by Dr. James S. Macgregor of Columbia University, 

 and he has kindly furnished the following explanation of 

 the data given by these tests: 



The specimens tested in tension, to determine their re- 

 sistance to being pulled apart, were circular in form and 

 had threaded ends. The load was applied in a direction 

 parallel to the grain. An extensometer, which is an instru- 

 ment for measuring small changes in length or strains occa- 

 sioned by an applied load, was attached to each specimen 

 during the test, and observations of elongations to one 

 ten thousandth of an inch recorded. The curve plotted in 

 Figure No. I shows the elongation resulting from the applica- 

 tion of a given unit load. By forming a ratio between a load 



*"The Standard Handbook for Electrical Engineers," McGraw Pub. Co., New York, 

 1908, Sec. 7, par. 374, p. 390. 



tWilliam Kent, "The Mechanical Engineers' Pocket Book," 8th ed.. New York, 1910, 

 p. 522. 



