616 Transactions of the American Institute. 



which is really an improvement on old methods, but in which it is 

 mere chance, and rarely the case, if it is the best that can be done 

 with the materials and for the requirements. Hence we see in 

 pavements as in other things but partial improvements, leaving a 

 wide margin for systematic invention. The requirements of a good 

 pavement are a uniform and smooth surface; a foothold for animals; 

 facility for removal for getting below it to the pipes, sewers, etc., 

 and for repairs; and lastly, durability; which, however, should 

 only be considered in connection with the question of economy and 

 advantages possessed; for a cobble-stone pavement is among the 

 most durable and cheap, while it is, at the same time, the most 

 objectionable pavement which could well be laid in other respects. 

 The incidental advantages of cleanliness, less wear and tear of 

 vehicles and horses, and freedom from noise, may be added. 



As to the question of any injurious effects of wooden pavements 

 npon the health, that has been decided by the most scientific autho- 

 rity of the country, and also by long practical experience and 

 obsei-vation, both in cities of this countiy and Europe; and in such 

 constructions as require antiseptic compositions to be used as pre- 

 servatives of the wood, or as cements, it has been fully proved that 

 they have a contrary effect, by acting as disinfectants. 



To secure these indispensable conditions of a good pavement for 

 a large city, certain peculiarities of construction are necessary; and 

 these conditions have been only partially met in the plans hereto- 

 fore introduced. Any construction in which small blocks are used, 

 necessitates the use of a continuous sub-sill or flooring, which makes 

 the pavement difficult of removal in getting below it; and which 

 construction, also, has the effect to displace or disturb portions of 

 the pavement within short distances of a heavy load moving upon 

 it, especially where there are small vacant spaces under it arising 

 from unequal settlement, or from the filtration of water through or 

 under it This is evidenced in experimental constructions in this 

 city, and elsewhere, in which a continuous sub-sill or flooring has 

 been used This construction, in which small blocl« are used with 

 so little bearing surface as to require a continuous flooring, is also 

 not so substantial, for the reason that the stability of the different 

 parts are dependent upon each other; for instance: if the bearing 

 of the sub-sills is rendered unequal from any cause, the blocks are 

 disturbed for some distance around. And asrain: the blocks beingr 

 so small, with so little bearing surface to rest upon, they are, of 

 course, more easily displaced by the action of vehicles, so as to 



