Prof. J. Perry on Liquid Friction. 



447 



As the deflexion is sufficiently nearly proportional to the 

 speed to allow of corrections by this rule when the cor- 

 rections are small, we have corrected the above observations 

 to the speeds 50, 40, 17J, 11^ ; and we obtain the following- 

 results : — 



Values of I. 



Values of n. 



50. 



40. 



171. 



11*. 



•5 

 2-5 

 5-0 

 7-5 

 9-9 



24 



67 

 112 

 165 

 200 



18 



54 



93 



132 



163 



8 

 25 

 40 

 57 

 73-5 



5 

 16 



27 



381 



51 



D and I were then plotted as the coordinates of points on 

 squared paper ; and it was obvious that for each value of n 

 these points lay very nearly in a straight line, and all the 

 straight lines passed through the point Z= — -0*8. It is curious 

 that the linear law should hold for such small values of I as 

 0*5 centim., and for high speeds as well as low speeds. We 

 shall presently see that some of these speeds are considerably 

 above the critical speed at which (4) ceases to represent the 

 motion. 



We may take it, then, that \=0*8 centim., which is greater 

 than the calculated value 0'52. The discrepance cannot be 

 due to the distance BH being small, for we have altered this 

 distance and found no perceptibly different results. As 

 already stated, it maybe due to some capillary surface action. 

 Taking <x = 1531 and \=0'8, we have (6) becoming 



/a = 0-769D/w(Z + 0-8) (7) 



Of course our results are consistent with our equations of 

 motion only so long as D/(Z+0'8) is proportional to n. 



Many observations have been made with this apparatus 

 during the last year on various liquids, under very different 

 conditions of temperature and speed and depth. We give 

 here a set made on sperm-oil. In all cases the bottom of the 

 trough was 0*5 centim. below the edge of the suspended 

 cylinder. 



Keeping the oil at a constant temperature we ran the trough 

 at a number of speeds, and repeated at other constant tempe- 

 ratures. The results are given in Tables IV. to XL 



When a temperature had to be taken the rotation was 

 stopped and a thermometer dipped about halfway down in the 

 oil, the reading being taken at the end of about half a minute, 



2 112 



