THE GREAT BRIDGE AND ITS LESSON'S. 341 



In no previous period of the world's history could this bridge have 

 been built. Within the last hundred years the greater part of the 

 knowledge necessary for its erection has been gained. Chemistry was 

 not born until 177G, the year when political economy was ushered into 

 the world by Adam Smith, and the Declaration of Independence was 

 proclaimed by the Continental Congress, to be maintained at the point 

 of the sword by George Washington. In the same year Watt pro- 

 duced his successful steam-engine, and a century has not elapsed since 

 the first specimen of his skill was erected on this continent. The law 

 of gravitation was indeed known a hundred years ago, but the intricate 

 laws of force which now control the domain of industry had not been 

 developed by the study of physical science, and their practical applica- 

 tions have only been effectually accomplished within our own day, and, 

 indeed, some of the most important of them during the building of the 

 bridge. For use in the caissons, the perfecting of the electric light 

 came too late, though happily in season for the illumination of the 

 finished work. 



This construction has not only employed every abstract conclusion 

 and formula of mathematics, whether derived from the study of the 

 earth or the heavens, but the whole structure may be said to rest upon 

 a mathematical foundation. The great discoveries of chemistry, show- 

 ing the composition of water, the nature of gases, the properties of 

 metals, the laws and processes of physics, from the strains and press- 

 ures of mighty masses to the delicate vibrations of molecules, are all 

 recorded here. Eveiy department of human industry is represented, 

 from the quarrying and the cutting of the stones, the mining and 

 smelting of the ores, the conversion of iron into steel by the pneu- 

 matic process, to the final shaping of the masses of metal into useful 

 forms, and its reduction into wire, so as to develop in the highest de- 

 gree the tensile strength which fits it for the work of suspension. 

 Every tool which the ingenuity of man has invented has somewhere, 

 in some special detail, contributed its share in the accomplishment of 



the final result. 



" Ah ! what a wondrous thing it is 

 To note how rnanj wheels of toil 

 One word, one thought can set in motion ! " 



But without the most recent discoveries of science, which have 

 enabled steel to be substituted for iron applications made since the 

 original plans of the bridge were devised we should have had a 

 structure fit, indeed, for use, but of such moderate capacity that we 

 could not have justified the claim which we are now able to make, that 

 the cities of New York and Brooklyn have constructed and to-day re- 

 joice in the possession of the crowning glory of an age memorable for 

 great industrial achievements. 



This is not the proper occasion for describing the details of this 

 undertaking. This grateful task will be performed by the engineer in 



