of Processes in the Fine and Useful Arts. 343 



Iron, cast - - 940000 



Iron, cast - - 963000 



Iron, cast - - 952000 



Mean of cast-iron, - 7.163 951600 



Bell-metal, - 8.531 818000 



On comparing these numbers with the modulus of elasticity 

 of the same substance, I find the modulus of torsion to be 

 Y^^th of the modulus of elasticity in metallic substances. — Phil. 

 Trans. 1829, p. 129. 



2. Results of Mr Rennie'^s experiments on the friction and 

 abrasion of the surfaces of Solids. 



The following are the results of a series of very valuable 

 experiments on friction made by John Rennie, Esq. 



The following table shows the amount of friction (without 



unguents) of different substances, the insistent weight being 



361bs. and within the limits of abrasion of the softiest stty- 



stance. 



Parts of the 

 whole weight. 



Steel on ice, - - - 69-81 



Ice on ice, _ . _ - 36.00 



Hard wood on hard wood, - - 7.73 



Brass on wrought iron, _ _ - 7.38 , 



Brass on cast iron, - - - 7.11 r 



Brass on steel, _ . - - 7.20 



Soft steel on soft steel, . - - 6.85 



Cast iron on steel, - _ - 6.62 



Wrought iron on wrought iron, - - Q.^Q 



Cast iron on cast iron, - - - 6.12 



Hard brass on cast iron, - - - 6.00 



Cast iron on wrought iron, - - 5.87 '. 



Brass on brass, . - - 5.70 



Tin on cast iron, - - - 5.59 



Tin on wrought iron, - - - - 5.53 



Soft steel on wrought iron, - - 5.28 



Leather on iron, - - - 4.00 



Tin on tin, - - - - 3.78 



