1835.] the Advancement of Science. 231 



smoothness, and hardness, and from the diminished resistance pre- 

 sented. It was a common error to suppose that the road on which 

 one was most easily drawn, was that on which a vehicle could pass 

 with facility, but, in reality, a carriage on a paved street required 

 less propelling power than on a macadamized road. It was also sup- 

 posed that the resistance of a road to a carriage merely depended upon 

 the nature of the surface, but this was not the truth, for much de- 

 pended upon the foundation, and if it was bad, the weight of the 

 wheels forced up the surface into little hills, over which there was 

 great difficulty in ascending. To constitute a good road, smoothness, 

 hardness, and evenness were necessary j and if any road could be 

 constructed perfectly in accordance with this description, no power 

 of draught would be necessary. Iron rail-roads approached most 

 nearly to perfection ; but though they possessed hardness they were 

 not entirely smooth ; and in the Liverpool rail-road, which had been 

 now used for some period of time, a passenger could tell, from the 

 inequality, when he was passing from one joint to another. The 

 force required for propulsion along a level rail-road, was about 9 lbs. 

 to one ton ; but supposing the rail-road to rise 1 foot in 250, although 

 the elevation could not, be discovered by the eye, yet a double force 

 of draught would be required. When the rise was more than 1 in 

 100, it exceeded the power of the machine, and then it was necessary 

 to use additional means of transit. The rise from Carlisle Bridge 

 to the Rotunda was about 1 foot in 500, and from Nassau Street 

 to Ann Street it was one in 90, and at this elevation no carriage 

 could go. There ought to be no sudden turns in rail-roads; no 

 curves perceptible in their bend. A sudden curve on an ordinary 

 road would be but a trifling objection, but when carriages were 

 travelling at the rate of forty miles, such an abrupt bend should 

 be avoided. In the Kingstown railway, there was only one 

 blemish : the suddenness of the curve near Kingstown ; and if the 

 rail- way was to be carried further on, as he hoped it would, the effect 

 would be felt greater, from the additional velocity not now required 

 at the termination of the line where the defect existed. He under- 

 stood that casual circumstances obliged the engineer to make the 

 draught curve of not less than half a mile, while it should have been 

 at least one mile. It was objected to railways that they were not 

 as good as common roads, because they did not admit of being made 

 where there were hills, but this was a silly argument, for illustrating 

 the subject by reference to a familiar instrument, he would say that 

 the edge of the razor would be blunted by what might not affect a 

 carving knife, because the razor approached nearest to perfection. 

 Dr. Lardner then referred to the mode of cutting tunnels to avoid 

 ascents ; and stated that on the railway between Birmingham and 

 London there will be seven tunnels, one of which will be a mile and 

 a half long, a second a mile long, and a third, at Primrose Hill, half 

 a mile long. Supposing that the power of steam had obtained its 

 maximum, when the rail-road from Liverpool to London would be 

 completed, the journey between the two places would be performed 

 in less than ten hours. It was not generally known that the weight 

 of the train considerably retarded the motion. He had travelled 48 

 miles an hour on the Kingstown rail-road, and upwards of 50 on the 



