THE EIFFEL TOWER. ' 145- 



which the stQiie (quarried at Chateau Laudon) has been 

 found to crush. 



3. Material. 



The possible materials which present themselves for such 

 a structure are 



Wood, Stone, 



Steel, Iron, 



and a combination of stone around an iron framework. 



Now, wood is too light to be safe in high winds ; stone is 

 very expensive, and heavier than metal in proportion to the 

 height attained; further, no mortar yet discovered will 

 stand more than 2,000 lbs. nominal, or say 200 lbs. working 

 pressure per square inch ; steel is too light, and, like wood, 

 too elastic, so that in a wind the rocking would tend to 

 dislocate the structure. Iron, which has none of these 

 defects, being heavy, rigid, and homogeneous, is therefore 

 indicated. 



It may here be remarked that the chief utility of the 

 tower lies in the fact that it gives us one more practical 

 example of the capabilities of iron. The ancients long ago 

 exhausted all the possibilities of stone. It remains yet to 

 be seen what iron can do, a problem to which the Forth 

 Bridge and Eiffel Tower are only partial solutions. It must 

 be remembered that the strength of iron is not an inherent 

 property, like the hardness of diamond or the suppleness of 

 bamboo, but an acquired one. The ores of iron can be 

 crushed to powder in the hand, or its nodules broken with 

 a light hammer. Wrought iron and steel, by processes 

 entirely artificial, have acquired the property of resisting 

 enormous strains. Within only the last few years the 

 efficiency of these processes has been vastly improved, and 

 feats of engineering made possible which were hardly 



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