two and four-tvhechd Carriages. 26$ 



Therefore we mall have as befcre R 35 2 '933 H&j oat 

 R' s= 412-026 lib.; confequently £■ — 3*696 feet, and g / =. 

 3-102 feet. 



Example III. 

 Seftion 32. 



After a feries of firnilar experiment! with fomewhat coarfer 

 and very moift red fand, I found $ - 43" 19', and c — T 5 T 

 inch at a medium. But it is to be obferved that the impref- 

 fions made by immerfing the fteel rod did not difappear as from 

 the above dry land, but remained after it was drawn out; and 

 therefore after each experiment I was obliged to make the fand 

 even and foft by (hatting it, and to render its furface ftnooth 

 by a (light prenure proportioned to the exacl meafurement 

 of the depth; by which means it loft a little of its natural 

 foftnefs. When I placed the rod again in the remaining 

 imprelfion it did not become deeper. Hence follows what 

 we arc taught by experience in general in regard to moid 

 fand, moid earth, thick mud, &x. that the hind-wheels 

 when they revolve in the ruts formed by the fore-wheels do 

 not make them deeper, and confequently experience no re- 

 lit lance from finking down ; fo that in the value of R, lec- 

 tion 26, found for four-wheeled carriages, in fuch cafes the 

 laft member (4 P + p) cos. a, fin. (3, tang. y\ vanifhes. 



Let us fuppofe then, as in the firtl example, feftion 30, 

 that the angle a = 4 the weight of the wheel?, p — 84 lib., 

 p> = no lib., 7T = 132 lib.; and their femidiameter in the 

 fame order, GO = 1$., 21, 24' inches, and h = 3 inches; 

 alfo let m»| n =.- ~\, /* m T ^, * = |, ttshifa, and g = 

 5 lib. If the load be P=- 900 Kb., and ddc zz T 5 T cubic inches, 

 we fhall have 



*'£ el V± o , * k'LLi 



If 



