Proceedings of the Polytechnic Association. 711 



speecli, which was rather a specimen of special pleading in behalf of 

 this particular scheme than an exposition of any mechanical or 

 engineering principles involved. The plan may be briefly stated 

 to contemplate the excavation of Broadway to a depth of about 

 seventeen feet, and then to replace the roadway as it now exists 

 by a firm and solid bridge, a new street being thus formed 

 nnderneath the roadway. At the sides of the roadway will be left 

 an area of five feet as now, protected by railings, and open except in 

 front of doors, and at each block circular stairways will lead to the 

 lower street. The sidewalks are to be relaid as now, except that next 

 to the street patent lights will be placed to the width of four feet 

 along the line of the street, which, with the areas, will give sufiicient 

 light to read in the cars with ease. The five-feet areas at each side 

 and the cross ventilation procured at the cross streets are expected to 

 give abundance of air. 



The lower street, restijng on the solid earth, will be devoted to the- 

 railroad and tM^o sidewalks. The sewers, and water, and gas pipes 

 will be placed just beneath the surface of the lower street, and may 

 thus be reached at any time without the trouble of digging now 

 experienced. The water and mud of the upper street will run into 

 the sewers through the hollow columns. 



With four tracks, the two inside ones are to be used for rapid 

 trains to accomodate through travel, going from the Battery to Har- 

 lem in about thirty minutes ; and the outside tracks, next to the 

 sidewalks, for slower cars, stopping as often as may be desired to 

 accomodate way travel. The inside trains running with great rapid- 

 ity and the outside cars running at as short intervals as necessary, 

 with the two branches from Union square, are expected to accomo- 

 date all the travel that will offer for many years. 



After deciding to resume this discussion the association adjourned. 



May 28, 1868. 



Professor S. D. Tillman, Chairman. 



The following notes on new discoveries and inventions were pre- 

 sented by the Chairman : 



The Dueometee. 

 The instrument for testing the hardness of metals by drilling is the 

 invention of M. Behrens, an Engineer of Tarbes in France. It ha& 



