I52 PNEUMATIC TIRE CH. X 



what unexpected to the mechanic. Instead of in- 

 creasing the draught even slightly, it has diminished 

 it, owing to the perfect elasticity of the air contained 

 in the tubular tire preventing any appreciable rising 

 of the weight of the carriage in passing over an 

 obstacle, the resistance merely forcing the air from 

 one part of the tube to another, and experiment 

 has shown (Michelin, p. 21) that the saving in 

 draught is greater as the speed is higher : for in- 

 stance, with the same spring vehicle : — 

 With iron tires : 



At a walk, 3 ms. pr hour, the traction was 48 pds pr ton. 

 ,, trot, 6. 5 ,, ,, ,, ,, , , 59 ,, 



,, fast trot, 9.4 ,, ,, ,, ,, ,, 77 ,, 



With pneumatic tires : 



At a walk, the traction was 48 pds pr ton. 



,, the other speeds, ,, ,, ,, 50 ,, 



The pneumatic tire, almost in exactly its present 

 form, was invented and patented in 1845, by R. W. 

 Thomson, of London. (English Patent Specifica- 

 tion, a.d. 1845, No. 10990.) Experiments made with 

 it, reported in The Mechanics Magazine, of March 

 27th 1847, gave the following results : — 



A carriage weighing 1050 pounds, running at 9 

 miles an hour, on a good macadam road, required 

 28 pounds of tractive force (53.3 pds per ton) with 

 pneumatic tires, and 45 pounds (85.6 pds per ton) 

 with iron tires. On broken stone, rough, the force 

 required was 38 pounds (72.3 pds per ton) with 



