Page:Report from the Select Committee on Steam Carriages.pdf/218



Mr. John Macneil. 6 September, 1831. an inch in depth. Now as this road is very little affected by wet, in consequence of its peculiar construction, and the care bestowed on its drainage, I attribute almost the whole of the diminution of materials to actual wear. On many roads, where the sides are weak, great injury arises from the crushing of materials, particularly by the action of waggon-wheels. In frosty weather, weak roads very frequently suffer more in one month than all the rest of the year. In such cases, the injury is caused by the wheels of Carriages, and not by the horses' feet.

If 30 lbs. be sufficient to move a Carriage of 21 cwt. 8 lbs. on a level platform, little affected by friction, and 266 lbs. be required to move the same Carriage up an inclination of 1 in 10, the pressure in the one case being exactly the weight of the Carriage, 21 cwt. 8 lbs. what would be the pressure on the road; or platform; on the inclination?—As the pressure on the horizontal is to the pressure on the inclined plane, as the length of the plane is to its base, we have this proportion, $$\sqrt{b^2 + p^2} : b :: \mathrm{W} : \frac{\mathrm{w}b}{(b^2 + p^2)\tfrac{1}{2}} =$$ the pressure on the plane. In this example, w=2360. b=10. p=1, which gives $$\frac{\mathrm{w}b}{(b^2 + p^2)\tfrac{1}{2}} = \frac{2360 \times 10}{\sqrt{100 + 1}} = 2349.5\ \mathrm{lbs.}$$ or 10$1⁄2$ lbs. less than the pressure on the horizontal.

Taking twenty miles near London, 150 lbs. appears to be the average force actually engaged in drawing the Carriage of 21 cwt. 8 lbs. including hills, would the force required to draw a carriage of 42 cwt. 18 lbs. be on an average 300 lbs. and so on in proportion; the extreme traction of the Carriage being 343 lbs. what on this road would have been the maximum force required to draw a Carriage of four tons weight?—It does not follow that because a Carriage is twice as heavy as another, that its draught would be twice as much; the resistance arising from gravity on the inclined planes would, abstractedly considered, be