478 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK iv. 



or trams, loaded with burdens too heavy to be moved by horses. In 

 1864 experiments were made at Nantes with a road-engine, con- 

 structed by one of the most experienced of French mechanicians, M. 

 Lotz. In August of the year following these experiments were 

 repeated at Paris, and gave interesting results. 



With a load of five to six tons the velocity of Lotz' locomotive 

 reaches ten miles an hour on a road in good condition ; it will draw 

 a load of 12 to 15 tons at the rate of 3J miles, ascending slopes 

 varying from 7 to 13 inches in a hundred. 



One of the disadvantages of this method of transport is the great 

 variation in the amount of work to be done by forces which remain 

 sensibly constant. Larmanjat's locomotive takes this difficulty into 

 account. For the large driving-wheels, going at the rate of ten miles 

 an hour, can be readily substituted two of smaller diameter, working 

 with the former and placed inside them. This substitution diminishes 

 the velocity of the engine, and if this be reduced by one half, the 

 force of traction will be doubled, and the locomotive can then over- 

 come obstacles which the slope or bad state of the roads may oppose 

 to its passage. An engine of this sort was shown at the Paris Exhi- 

 bition in 1867. It was of 3 horse-power. " It started from the Auxerre 

 terminus, drawing a heavy truck with low wheels, carrying a load of 

 about three tons, and with this load it was able, by the employment 

 of its small wheels, to ascend a long incline of 8 in a hundred with a 

 mean velocity of five miles an hour." Other experiments, made con- 

 tinuously in the suburbs of Paris, have been very favourable, it 

 seems, to this system. The view we give of M. Larmanjat's road- 

 engine (Fig. 322) is taken from nature, on one of the numerous trials 

 recently made in Paris in the Trocadero. 



We ought also to mention M. Albaret's, of Leancourt (Aisne), 

 road-engine, which has been tried for two years in the Departements 

 du Nord and the Jura, drawing loads of 12 tons on roads with inclines 

 of 5 or 6 in the hundred, with a maximum velocity of 3f miles an 

 hour, and that of M. Garret, which has drawn a diligence with 15 

 passengers from Auxerre to Avallon arid back at a mean velocity of 

 7 miles an hour. 



The English and Americans have not been behindhand in this 

 kind of research. They have made many attempts to solve practically 

 the question of steam-locomotion on ordinary roads. The difficulty 



