168 LECTURE XVIII. 



are usually received on a frame supported by a pivot, which allows them 

 to be turned with great ease. In particular situations, these waggons are 

 loaded by little carts, rolling without direction down inclined planes, and 

 emptying themselves ; they are also provided with similar contrivances for 

 being readily unloaded, when they arrive at the place of their destination. 

 The carriages used for drawing loaded boats over inclined planes, where 

 they have to ascend and again to descend, are made to preserve their level 

 by having at one end four wheels instead of two, on the same transverse 

 line ; the outer ones as much higher than the pair at the other end, as the 

 inner ones are lower; and the wheelway being so laid that either the 

 largest or the smallest act on it, accordingly as the corresponding part of 

 the plane is lower or higher than the opposite end. It is possible that 

 roads paved with iron may hereafter be employed for the purpose of expe- 

 ditious travelling, since there is scarcely any resistance to be overcome, 

 except that of the air, and such roads would allow the velocity to be 

 increased almost without limit. 



For removing earth from one situation to another, a series of baskets has 

 sometimes been hung on two endless ropes, moving on pullies of such a 

 form as to suffer the bars supporting the baskets to pass freely over them ; 

 the baskets being moved by means of a winch acting on the rope by a 

 wheel like one of the pullies. Sometimes also a series of little carts has 

 been connected by ropes, and drawn in a circle or oval up and down an 

 inclined plane. These methods may be adopted in making roads where a 

 hill is to be levelled, and the materials are to be employed in filling up the 

 valley below ; but in such cases two carts, connected by a cylinder or 

 windlass, are generally sufficient ; and they may be arranged in the same 

 manner as the carriages for removing boats on an inclined plane. 



LECT. XVIII. ADDITIONAL AUTHORITIES. 



Machine employed for clearing the Port of Toulon. Belidor, Architecture Hy- 

 draulique, ii. II. pi. 20. Ferguson on a Crane, Ph.' Tr. 1763, liv. 24. Redely- 

 kheid, Machine & creuser les Pores, fol. La Hague, 1774. Suspended Scaffolding, 

 Encyclopedic JMethodique, pi. iv. Peintre en Batimens. Hall's Crane, Trans, of 

 the Soc. of Arts, vol. xii. 



On Wheel Carriages. On the Benefit of High Wheels, Ph. Tr. 1685, xv. 856. 

 Lahire on the Magnitude of Wheels, Hist, et Mem. de Paris, ix. 116. Parent, do. 

 1712, p. 96. Reaumur, do. 1724. p. 300. Dupin de Chenonceau, do. 1753, H. 

 301. Emerson's Mech. p. 194. Boulard and Margueron on Broad Wheels, Ro- 

 zier's Jour. xix. 424. Jacob on Wheel Carriages, &c. 2 vols. 4to, 1773-4. Anstice 

 on do. 1790. Bailey, Plates of Machines approved by the Society of Arts, 2 vols. 

 fol. 1782. Rizzetti, Riforma de' Cam di quattro Ruote, Trevigi, 1785. Edgeworth, 

 Tr. R. Ir. Aca. 1788, ii. 73. Lamber, Hindenburg's Archiv, ii. 51. Grobert sur 

 les Voitures a deux Roues, 1797. A. Young, Annals of Agriculture, xviii. Fuss, 

 Versuch einer Theorie des Widerstandes zevey-und-vier-radiger Fuhrwerke. Co- 

 penhag. 1798. Ph. Mag. xiii. 115. Anderson's Institutes of Physics, quoted by 

 Cavallo, Nat. Ph. Cumming on Conical Wheels, 4to, 1804. Board of Agriculture, 

 ii. 351. Repertory of Arts, xiii. 256. Imison's Elements of Science and Art, 

 2 vols, 1803, i. 129. Ferguson's Lect. by Brewster, ii. 296. 



