84 A heller to the Dullin Society 



l.ittcr end of last May; to which I beg leave to subjoin stich 

 practical observations as have occurred to me on the subject. 



For the accuracy of the facts, the public will of course impli- 

 citly depend upon the Report of the committee. For the de- 

 ductions that are here drawn from them, I alone am answer- 

 able. 



The first experiments that were tried, were to ascertain the 

 friction of three different axle-trees: 



A straight axletree, 



CoUinge's patent axletree, 



And an axletree belonging to Messrs. Bourne, mail-coach 

 proprietors. 



These experiments were tried with two-wheeled carriages, 

 moved by weights and pulleys. The carriages were placed first 

 upon u road of wood, afterwards upon one of iron, perfectly 

 horizontal: the amount of the weight which put each of them 

 in motion, was considered as the measure of the friction. 



The weight of tlie wheels of each carriage was deducted from 

 the gross weight, because their weight does not afl'ect the fric- 

 tion of the axletree on which they turn. 



The weight of each carriage, after this deduction was made, 

 was 7 cwt. 3 qrs. 23 lbs. that is 890 pounds avoirdupois ; the 

 weight of the wheels and axletree may be taken at a medium at 

 250 pounds. 



On the 

 wooden road. On iron. 



The carriage on the straight axletree 



was drawn by 191bs. ■ 11 lbs. 



The carriage on the patent axletree, 



drawn by 15 lbs, 11 lbs. 



Ditto on Mr. Bourne's axletree, drawn 



by 21 lbs. 121bs. 



The diiferences that appeared in these experiments upon the" 

 wooden and iron roads, arose from the position of the tire of the 

 wheels, which caused the tire to sink into, or adhere more or 

 less to the wooden road; the difference where running on the 

 iron road was inconsiderable between the compared axletrees. 



The wheels of the two former carriages were common dished 

 wheels ; the latter with Mr. Bourne's axletree had wheels with 

 spokes inclined in opposite directions, or, as they are called, 

 double-dished wheels*. To estimate the power necessary to 



overcome 



* Wiiere wliecln m-p. so dished or splayed, as to throw tlie sol* of the 

 wlucl, :is it sets upon tiie proiuid, beyoiMi the line let fall peipendicular'v 

 fioin the end of the arm of the axletree to the »rouiul, tlu: box of the nave 

 will pinch the under part of ilje arm of the astletreenear the linch-pin, and 



vn'A 



