VOL. XV.] PHILOSOPHICAL TRANSACTIONS. 115 



rod a little more than -|- an inch thick. 4. 31 lb. drew them over a square rod 

 4. an inch thick. 5. 12 lb. drew the hinder wheels over the larger square rod. 

 The string being laid under the axle, viz. -|- of an inch lower than before; then, 



6. 29 lb. drew the lesser wheels over the larger square rod. Then the 1 larger 

 wheels being put on instead of the lesser, and the string lying over the axle, 



7. 3 lb. drew the model on the table. 8. 15 lb. drew the fore wheels over the 

 round rod. Q. 25 lb. drew them over the larger square rod. 10. The string 

 lying under the axle, 16 lb. drew them over the least rod. 1 1 . 23 lb. drew them 

 over the round rod. 12. 23 lb. drew them over the larger square rod. 13. 13 lb. 

 drew the hinder wheels over the larger square rod. 



All these experiments, were tried twice at least, and most of them 3 or 4 

 times over. In all of them the lead was laid exactly on the same part of the 

 board; yet, when the lesser wheels were taken off, the lead did not lean so 

 much forward, so that the hinder wheels were somewhat more pressed than 

 before. 



By comparing the 2d, 3d, and 4th experiments, with the lOth, lith, and 

 12th, it appears how much more easily a waggon, &c. might be drawn on rough 

 roads, if the fore wheels were as high as the hinder, and if the thills were fixed 

 under the axle. Such a waggon as this would also be drawn more easily were 

 the wheels cut in clay, or sand, or any soft ground; besides, high wheels 

 would not cut so deep as low ones. Some other advantages are mentioned by 

 Dr. Wallis. 



It is true, low wheels are better for turning in a narrow compass than high 

 ones; but it seems probable that waggons with 4 high wheels might be so con- 

 trived, that there should be no great inconvenience in that respect ; at least 

 such waggons as seldom have occasion to turn short, as carriers' waggons and 

 the like. 



The difference observed in the 8th and 11th experiments, is agreeable to 

 what is said by S. Stevinus and Dr. Wallis, viz. that if a coach, &c. must be 

 drawn over rough uneven places, it is best to fix the traces to the coach lower 

 than the height of the horses shoulders. 



14. A table, 2^ feet long, was set with one end Q\ inches higher than the 

 other end, and the model being loaded as before, less weight by 6 ozs. drew it 

 up the table when the 4 larger wheels were on, than when 2 larger and 2 less 

 were on. The reason of which, as given by Dr. Wallis and other writers on 

 mechanics, is, because in the first case there was almost the same direction of 

 the motion of the model and of the string that drew it; but not in the 2d 

 case when the fore axle was so much lower than thetop of the pulley. 



a 2 



