Page:Popular Science Monthly Volume 2.djvu/633

Rh to drain off the rain-water. The powdered asphalt is then spread over the surface, to a depth of 16 to 20 inches (according to the amount of traffic), and stamped down. Then a heavy roller is drawn over it.

With regard to the danger of horses slipping and falling on the smooth surface of the asphalt pavement, the following facts are of interest:

At Lyons, which has long had mastic roads, a number of cavalry-horses fell on a street of compressed asphalt. This accident arose from the circumstance that the asphalt had been laid on an old macadamized road, and had therefore that considerable arch which is unnecessary and dangerous for the asphalt road. The cavalry riding in a long line, those horses near the side of the road slipped on the steep incline.

At Marseilles, where the asphalt roads from the harbor to the town were made with a very gentle curve, there has been no increase in the number of accidents, though the traffic is enormous. A very slight arch of the road is quite sufficient to allow the rain to run off from such a smooth surface.

It is also not advisable to lay the asphalt on any street with a gradient greater than 1 in 60, though in London some streets having a gradient of 1 in 57, and even to 1 in 46, have been covered with asphalt without any apparent danger. It is of course extremely difficult to get any accurate information about the number of accidents on the streets, general vague impressions being worthless; but in Paris the number of horses which were observed to fall in the Rue Neuve des Capucines, during two months, was as follows: In the former, which was paved with sandstone, in blocks, from Fontainebleau, one horse in 1,308 fell; on the latter, which was covered with asphalt, one in 1,409, so that the balance was in favor of the asphalt.

In snow or frost asphalt is not so slippery as granite, being in itself warmer, and also more easily warmed by the slightest rays of the sun; hence, the ice is more slow in forming, and quicker in melting, than on granite.

It has been proved that the greatest number of accidents to horses happen when the asphalt is not cleaned, for the surface is never muddy or greasy, except with foreign matter, and this ought to be constantly washed off with water, which is plentifully laid on in Paris, and to some degree in London. At any points where this cannot be done, a slight sprinkling of coarse sand will prevent the horses slipping. This is only a temporary remedy, but valuable in case of emergency. It is one of the great advantages of asphalt, however, that it is so easily and cheaply cleaned.

In case of a conflagration, the asphalt pavement will not help to spread it. In London heaps of wood were set fire to on asphalt pavements, but, when the embers were raked away, there were only a few weak flames seen issuing from the asphalt, and they went out of their own accord in a few moments.