. American highways; a popular account of their conditions, and of the means by which they may be bettered . ^ which needs to be checkedby any considerable exercise of power; for all the energythns nsed is directly applied to the destruction of thecostliest part of the way. The damage done by the pressure of the wheels on awell-built Macadam road is usually much less than is in-flicted by the shod feet of horses, especially where the shoes. Fig. 14. —Showing wagon-wheel pressed into thesurface of a dirt road, enlarging the area of con-tact and impeding the forward movement of thevehicle. are p
. American highways; a popular account of their conditions, and of the means by which they may be bettered . ^ which needs to be checkedby any considerable exercise of power; for all the energythns nsed is directly applied to the destruction of thecostliest part of the way. The damage done by the pressure of the wheels on awell-built Macadam road is usually much less than is in-flicted by the shod feet of horses, especially where the shoes. Fig. 14. —Showing wagon-wheel pressed into thesurface of a dirt road, enlarging the area of con-tact and impeding the forward movement of thevehicle. are provided with the usual calks at toes and heels. Thestress applied by the tires is wholly downward; when theroad has the normal covering of dust this acts as a cushionto distribute the pressure. If the wheel be of considerablediameter, say four feet or more, the area of the work mayhave a length of two or three inches at any moment of theaction. Though the time during which this pressure isaccumulated seems short, being, in fact, only a smallfraction of a second, it is long enough to permit the elastic 168 AMEBIC AN HIGHWAYS mass to be slightly compressed, so that it fits in a measureto the curve of the tire and so sustains the weight withoutrupturing the cement which unites the fragments of is quite otherwise with the blows which the feet ofdraught animals apply. These strokes are delivered sud-denly, so that the bed has
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1896
