86 MECHANICS. 



with eight miles, 1 6 pounds with nine miles, 9 pounds 

 with ten miles, 4 pounds with eleven miles ; 1 pound 

 with twelve miles, and at the speed of thirteen miles 

 per hour he will not be able to exert any power. 



On a rail-way the ease of draught is six times 

 greater than on a common road. 



On an ordinary canal one horse with a boat will 

 be sufficient for every 30 tons. 



A steam engine consumes about 20 feet of steam 

 per minute for every horse power. 



Carriage Springs. 



Springs of carriages convert all percussion into 

 mere increase of pressure : that is to say, the colli- 

 sion of two hard bodies is changed by the interposi- 

 tion of one that is elastic into a mere accession of 

 weight. It is probable that under certain modifica- 

 tions, springs may be applied with great advantage 

 to the heaviest waggons. 



In surmounting obstacles a carriage with its load 

 being lifted over, the springs allow the wheels to 

 rise, while the weights suspended on them are scarcely 

 moved from their horizontal level. 



Steam Engines. 



One of the largest yet constructed is now in action 

 at the United Mine in Cornwall. It raises 80,000 

 pounds 100 feet high per minute, with about 30 

 pounds of coal per minute. It is equivalent to about 

 the power of 250 horses. 



The steam engines in England represent the power 

 of 320,000 horses, equal to 1,920,000 men, and being 

 in fact managed by only 36,000 men, add conse- 

 quently to the power of our population 1,884,000 

 men. Mr. Watt's great improvement was condensing 

 the steam in a separate vessel, where a vacuum was 

 obtained by the continued application of cold water, 



