two and four-wheeled Carriages. II? 



Circular inequalities. But, as level as well as inclined roads 

 covered with fmall eminences and interfered with circular 

 depreflions, as far as the comparative maximum of refinance 

 is concerned, belong to inclined roads, and may be confi- 

 dered as fuch with an increafed degree of inclination, the 

 angle of inclination may be taken into the calculation with- 

 out much difficulty 5 confequently thefe properties require no 

 particular divifion. 



Sefiion 4. 



But, though this natural divifion of all the different kinds 

 of roads into three principal claffes will facilitate a com- 

 parifon between two-wheeled and four-wheeled carnages in 

 regard to the refiftance which they oppofe to the moving power 

 on each kind of road propofed, which is properly the object 

 of this refearch; it, on the other hand, appears difficult to 

 give a fatisfa&ory anfwer to the firft part of the queftion, 

 and to deduce, from mechanical principles, the ratio of the 

 moving power to the refiftance. The latter, indeed, can be 

 determined a priori from ftatical principles; but this is not 

 the cafe with the former, which, on account of the endlefs 

 difference in the ftrength of animals, and the various modi- 

 fications of this ftrength on different roads, can be deter- 

 mined only by experiments, and even then the refult will 

 be merely an approximation. 



Se&ion 5. 



In the following determinations, however, that I may be 

 able in fome meafure to compare. each kind of refiftance with ■ 

 the moving power, I (hall premife the following principles : 



ift, That the weight M, equal to one pound, (Plate II. 

 fig. 1.) freely fufpended from a rope pairing over the fixed 

 pulley C, is the heavieft that an animal ftanding on the 

 level plain AB can draw or fuftain during the period of t 

 hours. 



2d, That G is the greateft velocity with which the above 

 animal, without bearing any burthen or drawing any thing 

 after it, can travel for the period of t hours along a road of 

 any given nature; fo that, in regard to this animal, the ve- 

 locity G will be fometimes greater and fometimes lefs, ac- 

 cording to the nature of the road. 



Now, if M and G, in regard to the animal which we 

 fuppofe to be employed, and in regard to the road on which 

 the burthen is' to be carried, be known by experiments, we 

 fhall have a determinate meafure of the moving power, as 

 we know that the propofed animal can drawon the propofed. 

 road during the period of t hours, with the velocity g, a freely 



I 2, fufpended 



