PRESENT PROBLEMS OF TECHNOLOGY 577 



years ago. Then, steel rails were unknown and the durability of 

 the wrought-iron rails, which had supplanted those of cast-iron, was 

 limited in some instances to a few months only, but at this critical 

 period the invention of the Bessemer pneumatic process, followed 

 by Gilchrist. Siemens-Marten, and others, supplied an urgent neces- 

 sity as to quality; the various inventions of George and John Fritz, 

 Alexander Holley, William R. Jones, Nasmyth, Nobel, Krupp, and 

 many others met the demands for quantity, while the develop- 

 ment of commercial channels and establishment of improved plants 

 at strategic points has reduced the cost and increased the output to 

 such an extent that there is no retardation as yet visible in the curve 

 of progress so far as the quantity is concerned. The last fiscal year 

 (1902) shows an increment of 9626 miles of railroad in the country 

 which exceeds that of any year since 1890, so that the demand for con- 

 struction material continues to be one of the problems of the present. 



Especially is this the case with wooden cross-ties having a life 

 of only from seven to ten years. They require frequent renewals at 

 the expense of our hard-wood forests, with incidental injury to the 

 entire country from denudation, causing rapid erosion of uplands, 

 floods, and barren wastes. Therefore the recently established policy 

 of irrigation and reforestation has come none too soon to check the 

 evils of the wholesale slaughter of our forests. 



The increasing paucity of timber and the greater strength, dur- 

 ability, and economy of the metals have led to their rapid substi- 

 tution for the vegetable fibers, in most of the engineering struc- 

 tures, but the tendency is now returning strongly to the use of stone, 

 brick, or concrete wherever they are practicable and available, as 

 the best material for biidges and buildings. Where they cannot 

 be secured, artificial concretes and cements are frequently used 

 either singly or in combination with the metals in the form of mesh- 

 ings for imparting tenacity. Although much progress has been made 

 in this class of material, it yet remains to discover the secret of the 

 ancient compounds as instanced in the remarkably durable water- 

 tanks of the Arabs, built at Aden about 600 years B. c., and still in 

 a perfect state of preservation. 



Notwithstanding the extended researches made upon the pro- 

 perties of material for structural purposes, much still remains to 

 be discovered. One of the latest investigations made as to the use 

 of pure sand, encased in light sheet-metal tubing, merely to pre- 

 vent it from flowing, reveals some astonishing results in transmit- 

 ting pressure in the form of beams subjected to cross-strains, or in 

 the form of columns carrying heavy loads. These investigations, 

 conducted by Prof. A. V. Sims, may result in important economic 

 changes in engineering structures in the near future, when reduced 

 to a practical basis. They cannot be elaborated in this paper. 



