ABRASION OF THE SURFACES OF SOLIDS, 



169 



N 



In an experiment made on one of the corn mills recently erected for His 

 Majesty's victualling department at Deptford, it required tV of the weight of 

 the mass to overcome the inertia and friction of the bearings and tangential 

 surfaces. In this instance the pressures of the different parts of the machine 

 varied from 28lbs. to 8 cwt. per inch area, and the velocities of the surfaces 

 from 50 feet to 120 feet per minute. 



REMARKS. — It has been customary to deduct one fourth of the power expended for friction. This 

 allowance taay maintain in machines newly set in motion. When the bearings have been equalized 

 .ind the rubbing surfaces extended by the abrasion of the irregularities, the friction will be diminished 

 and the movements of the machine be more steady. But when the bearings are properly propor- 

 tioned to the weight of the parts of a machine, and their surfaces kept from contact by unguents, 

 a much less allowance may be made. 



Several experiments were made by giving motion to a fly wheel and a grindstone of known weights 

 and revolutions in a given time, and then counting the revolutions after being detached from the 

 power ; but owing to the resistance of the air, and the bearings being too small, the results were unsa- 

 tisfactory. 



Table XV. Showing the amount of friction (without unguents) of different 

 substances, the insistent weight being 36lbs. and within the limits 

 of abrasion of the softest substance. 



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 



Brass on steel 7.20 



Soft steel on soft steel 6.85 



Cast iron on steel 6.62 



Wrought iron on wrought iron . . . 6.26 



Cast iron on cast iron 6.12 



Hard brass on cast iron 6.00 



Cast iron on wrought iron 



Brass on brass . . 



Tin on cast iron 



Tin on wrought iron 



Soft steel on wrought 



Leather on iron 



Tin on tin . 



Granite on granite . 



Yellow deal on yellow deal 



Sand-stone on sand-stone 



Woollen cloth on woollen cloth 



Parts of the 

 whole weight. 

 5.87 



5.70 

 5.59 

 5.53 

 5.28 

 4.00 

 S.78 

 3.30 

 2.88 

 2.75 

 2.30 



These results are collected from the different Tables, but the comparison 

 may be made by selecting other values within the limits of abrasion for a mi- 

 nimum. 



General Conclusions. 

 From what has been stated hitherto it is obvious, — 



1st. That the laws which govern the retardation of bodies gliding over each 

 other are as the nature of those bodies. 



MDCCCXXIX, z 



