AMERICAN INSTITUTE. 663 



tliemseves temporarily, by using a rough road for a short period, 

 the stones will become united into a compact mass, which the 

 gravel prevents, and thus form a permanent and admirable road. 

 The force of traction per one ton on the former would be about 

 150 lbs.; on the latter 50 lbs.; when smooth 35 lbs. Road- 

 makers should keep in view that the principal object most 

 desirable on all roads is the diminution of the actual resistance a 

 vehicle opposes to the tractive power, which is accomplished by 

 making the surface of the road perfectly smooth. Eesistauce to 

 the tractive power is greater on a soft than a hard road. This 

 may be demonstrated on mathematical and mechanical principles. 

 The traction is always proportional to the road, and inversely 

 proportional to the wheel's diameter. In Broadway, as now 

 paved, the resistance is entirely independent of the width of the 

 tire if it is more than three inches. Traction increases with 

 velocity. When roads are made with gravel alone, roadmasters 

 generally insist upon having it sifted until it is perfectly clean. 

 From experience I have come to the conclusion that this is wrong, 

 from the fact that no binding material is left to hold the thousand 

 fragments together, and the gravel cannot become solidified im- 

 mediately, but if the adhering loam is permitted to remain on, 

 the interstices between the gravel is filled up at once, and the 

 road may be opened for traffic. Engineers usually endeavor to 

 make a road as level as possible, without taking into considera- 

 tion the fact that a horse will travel with much more ease on a 

 road alternately ascending and descending, than on one perfectly 

 level, or gradually ascending. 



Our fourth class consists of pavements made of blocks of wood, 

 which have been tried in Europe, Russia and America, with bad 

 success, on account of the immense sums of money annually 

 required to keep the blocks in repair. This was owing to the 

 want of proper foundations. They were likewise found slippery 

 at certain periods of the year. Still this might have been easily 

 obviated by a plan that I will suggest before I complete my 

 remarks. 



