jzo On the Rejiflnnce experienced ly 



of this clafs, and in regard to two-wheeled carriages, has to 

 overcome a refiftance compounded of thefe three parts: 

 R 5: (jt. x P cos. a + (P -f e -f- m) fin. x. 



III. Comparifon between tbefe two Kinds of Carriages. 



If a o, then is R = 4 (m + n) * P, and R' = p x P ; 

 Confequently, R < R' when m + n < 2p. That is : on folid, 

 fmooth, horizontal roads, four-wheeled carriages are better 

 than two- wheeled when the axles and wheels are fo con- 

 ftruclcd that the fum of the exponents of the ratio of their 

 diameters in the former, is lefs than double the exponent of 

 the ratio of the diameters of the axles and wheels in the latter. 

 Seclion 14. 



If£-f/>'=eP + 9r,then will R < R', when p + n < 2u. That 

 is: on folid, fmooth, inclined roads, four-wheeled carriages 

 are to be preferred to two-wheeled carriages under the above 

 conditions, provided alfo that the weight of the fore and hincj 

 wheels in the former is equal to the fum of the weight of the 

 wheels and of the overweight * in the latter. 

 Seclion 15. 



If m + n = 2/jc, then is R < R', when p -f- p' < sP + $r t 

 That is: on folid, fmooth, inclined roads, four-wheeled car- 

 riages are preferable to two-wheeled carriages when the ratio 

 of the diameters of the axles and wheels is fuch that the fum 

 of the exponents in the former is equal to double the expo- 

 nents in the latter, and provided alfo that the weight of the 

 wheels of the four-wheeled carriage is lefs than the weight of 

 the wheels and the overwe'ight in the two wheeled carriages. 

 Seclion J 6. 



From the comparifon, in general it remits, that for this 

 kind of roads four-wheeled carriages ought to be preferred to 

 'two- wheeled carriages. 



1 ft, When in regard to the proportion between the wheels 

 $nd the axle-trees, 



m + n — 2p (sP 4- t ~- p— p') tang, a 



#d, When in regard to the weight of the wheels, 



P+p' — tt< eP— **v;r *£i-2 . 



' * tang, a 



3d, When in regard to the weight of the load, 

 p > (P+P' -*) tang.a 



£ tang, a — ~ A (m-f « — 2p,) * 



* That which arifes from the centre of gravity being thrown behind 

 the axle. See fedtion 11, and alfo fig. 3. 



4&i 



