1832.] 



Progress of Mechanical Science. 



429 



Mr. James M'Adam acquaints us with the fact of the legislature having obliged 

 the tires of all wheels to be free from projecting knobs or nails — a great improve- 

 ment; he looks to great benefit to the roads from dispensing with horses: weigh 

 bridges are now universally abolished, the effect of carts upon roads being mainly 

 proportionate to the number of horses, according to which the toll is now levied. 



Mr. John Macneili. furnished a variety of very useful experimental tables of 

 the pressure of various carriages upon an inch surface of road ; — the weight neces- 

 ary for their draught with different velocities and on different inclinations ; — and 

 he expence per mile for the same. The experiments of the second table were 

 conducted under Mr. Telford, with a machine invented by his assistant Mr. 

 Macneill for measuring the force of traction, or the labour of horses in drawing 

 carriages. The following are the general results in a tabular form. 



Results of experiments made with a stage-coach, weighing, exclusive of passengers, 

 18 cwt. on the same piece of ground with different inclinations. 











Expence. of drawingj 

 one ton per mile 

 in a waggon at 2^ 



Inclination. 



Rate of tra- 

 velling. 



Force requir- 

 ed. 











miles per hour. 











pence. 



1 in 20 



6 



miles 



268 lbs. 



22.83 



1 in 26 



6 



>> 



213 





1 in 30 



6 



it 



165 



18.55 



1 in 40 



6 



>> 



160 



16.79 



1 in 600 



6 



}> 



111 



12.66 



horizontal 









12.36 



1 in 20 



8 



}> 



296 



[Expence of draw- 



1 in 26 



8 



>J 



219 



ing one ton per 



1 in 30 



8 



5> 



196 



mile in a four- 



1 in 40 



8 



J> 



166 



horse stage, at 10 



1 in 600 



8 



>> 



120 



miles per hour.] 

 d. 



1 in 20 



10 



5» 



318 



50.47 



1 in 26 



10 



5> 



225 





1 in 30 



10 



J> 



200 



44.15 



1 in 40 



10 



>> 



172 



41.25 



1 in 600 



10 



>> 



128 



33.59 



horizontal 



10 



11 



? 



32.93 



The following are the same engineer's accurate measures of traction, or resis- 

 tance, on different qualities of road, which are directly opposed to M'Adam's 

 theory of road-making, as applied to cities, though not to country. 



1. — On well-made pavement, the draught (of each horse ?) in a waggon 



weighing about 21 cwt. is 33 lbs. 



2. — On a broken stone surface or old flint road, 65 



3. — On a gravel road, 147 



4. — Qn a broken stone road upon a rough pavement foundation, 46 

 5. — On a broken stone surface upon a bottom of concrete, form- 

 ed of Parker's cement and gravel, „ 46 



No description is given of Mr. Macneill's dynanometer, but Mr. Telford 

 speaks of it in great commendation. 



