82 THE POPULAR SCIENCE MONTHLY. 



ly, was paid to the construction of roadways. Cobble-stones were re- 

 sorted to for paving-purposes, since they were easily obtainable in the 

 alluvial plains in which most modern cities are founded. They were 

 succeeded by irregular quarried stones of such quality as was within 

 easy reach ; then by larger square blocks, mainly of trap-rock or gran- 

 ite, such as were thought necessary in streets with heavy traffic. But 

 experience has proved that the jarring against them compelled the 

 construction of heavier wagons, and that their peculiar smoothness by 

 wear caused the horses to fall, and so this material was modified to 

 uniform oblong blocks in narrow courses. These, after severe tests, 

 have maintained a truer surface, have been found to offer a greater 

 resistance against wear, to lessen the noise, and to decrease consider- 

 ably the number of accidents to horses. They are called, in common 

 with the former, Belgian blocks. 



A most important sanitary feature, almost entirely neglected be- 

 fore the rapid concentration of population in the cities, now demanded 

 attention. The cubical stone blocks are displaced under the prodi- 

 gious traffic, the corners and edges are worn away, the surface gets 

 to be irregular, the joints are widened. The filth of the streets 

 gathers in ruts and joints, is recruited constantly by new acces- 

 sions of urine, horse-dung, and silt, and, diluted by the rain, it fer- 

 ments, and forms a putrescent organic mire, becoming in course of 

 time a source of noxious miasmas. In hot and dry weather these 

 nauseating deposits pass into the atmosphere in the form of unhealthy 

 vapors, or, pulverized and drifted by the wind, cause inconvenience 

 and poison our lungs. Indeed, in repairing old pavements, a black 

 layer of ground, saturated with sulphuretted hydrogen, is found be- 

 low the stone blocks, and bears witness to the infection of the sub- 

 soil by the soakage of contaminated water. Prof. Tyndall has estab- 

 lished by experiments that a large proportion of the particles of dust 

 in the rooms of London houses is of organic origin, and other experi- 

 ments have demonstrated that horse-manure, in a state of decomposi- 

 tion, is a permanent ingredient. 



Vapors still more noxious than those from the road-bed of the 

 streets rise from the gutters, the subsoil of which is saturated to a con- 

 sidei-able depth by more concentrated matter of the described compo- 

 sition, and also from the surface of alleys on which are the houses of 

 great numbers of people of limited means. Crowds of dirty children, 

 whose tender lungs breathe the air immediately over this miasmatic 

 soil, here contract constitutional predispositions, which doom them to 

 a languishing and miserable life, and render them an easy prey to 

 epidemics. This infection of the subsoil has been prevented, .with a 

 certain defjree of success, bv foundations of concrete. There is still 

 another feature of stone pavements in the heart of cities, which affects 

 the inner man more than the physical frame, viz., the rattling and 

 noise, imder heavy traffic, accomj)anied, in alluvial soil, by vibrations 



