84 THE POPULAR SCIENCE MONTHLY. 



ufacture in the show-windows, and haunting the anxious housewife in 

 kitclien, pantry, and cellar. The devoted denizen finds but a partial 

 protection against the shocking nuisance, when he mixes this dust with 

 an abundance of water by sprinkling the street. 



A modification of the macadam is the Telford road ; it consists 

 of a bed of firmly-wedged quarry-stones, with an even surface as a 

 foundation, upon which a layer of larger and a layer of smaller broken 

 stone, mostly trap-rock, are spread, each being rolled by horse and 

 steam rollers. Upon the well-compacted surface a binding of screened 

 gravel is applied, moistened and rolled in, so as to present one solid 

 mass, which, while hard and durable, yet retains some elasticity. This 

 variety, superior for country-roads, though still open to the vital ob- 

 jection of dust, is equal in price to the costly modern city pavements, 

 and therefore has found but a limited application within city limits 

 for instance, on the Boulevards of New York. 



Wood pavements which, at one time, were much used in Britain, 

 especially in London, and also in New York in 1835 and 1836, but 

 were abandoned for weighty reasons, and especially on accoimt of 

 their rapid decay, were revived in the rising cities of the great West, 

 notably Chicago, where stone was scarce, lumber was cheap, and a 

 porous, sandy subsoil retarded the decay of the perishable wood- 

 blocks by dry rot from below, as happens on retentive soil. These 

 wood pavements, smooth, noiseless, and advantageous for traction, 

 were rather hastily adopted by municipal committees or boards in 

 Eastern cities, where the conditions were difierent, and where decom- 

 position commenced after two or three years' use. The heavy profits 

 made induced a desperate fight in their favor by interested parties, 

 a renewed effort in behalf of "treated" wood gave them a respite 

 and a second harvest before final disuse, which was accelerated, how- 

 ever, by the overwhelming complaints of the offensive and unhealthy 

 effluvia emitted from them ; so that, in a sanitary point of view, the 

 advantage of the absence of stone-dust was much overbalanced by the 

 decomposition of the material itself. 



The wood-blocks during treatment have been mostly impregnated, 

 by pneumatic processes, with chloride of zinc, sulphate of iron, or 

 oily, creosotic substances ; and, though railroad-sleepers, telegraph- 

 poles, etc., have been satisfactorily preserved through these agencies, 

 such methods have failed, for various causes, to render an equivalent 

 for the expenses incurred in treating the paving-blocks. But the pa- 

 tience of the people is not yet exhausted, and, in Northwestern cities, 

 a new and costly revival is being arranged by the substitution of sul- 

 phate of copper for impregnation, a substance used in France, under M. 

 Boucherie's patent, for thirty-five years past. The District of Colum- 

 bia has been preeminently the experimental ground for treated wood 

 pavements. An investment of about $5,000,000, a sum far in excess 

 of that in any other city of the globe, has been made there within 



