DISC FKICTION 



191 



In the following Table the results from a series of 9-inch discs in a 

 painted cast-iron casing with | inch side clearance, and running at 1,500 

 revolutions per minute, are compared with those obtained from similar 

 12 inch discs with similar (0*825 inch) side clearance, the latter results 

 being obtained by interpolation from those obtained experimentally with 

 f inch and with 1 J inch clearance. As the same casing was used through- 

 out, the radial clearance was not, however, similar in the two cases, being 

 respectively \ inch and 2 inches. 



The results show that the resistances in these experiments are propor- 

 tional to the (n -\- x) power of the radii, where x, instead of being equal 



EFFECT OF A VARIATION IN DIAMETER. 



to 3, has the values 2*782, 2*765 and 2*741 in the respective series. 

 From the last column of the Table it appears that the resistance of the 

 smaller disc is approximately 6 per cent, greater than would be the case 

 if x were equal to 3, i.e., if the radial clearance were proportional to the 

 radius, so that a given increase in radial clearance would appear to have 

 approximately the same effect as a corresponding increase in side clearance. 



Results of Dr. Unwin's Experiments.- For the sake of comparison the 

 main results of these are given in the following Table. In them the speed 

 varied between 66 and 350 revolutions per minute, and for the values 

 here given the virtual radius of the disc was 0*8488 foot. 



From the Table it appears that although the differences between these 

 values of "/" an ^ " n " and those obtained by the author are in some 

 cases large, the values of the friction per square foot as calculated for the 

 two speeds in every case agree fairly closely. 



