[barnes] 



SPHERES MOVING THROUGH WATER 



59 



In the case of zinc the surface was coated with a thin layer of 

 white vaseHne to prevent the formation of bubbles. 



The magnesium ball had to be coated with celluloid lacquer to 

 prevent the action of water on the metal. 



The following table contains the results of the observations. 



Table. 

 Table showing accelerating force on metal spheres in water. 



In the fourth column the time of swing in water is given. The 

 observations are taken to an accuracy of about 1 part in 5000, but 

 it is not possible to claim this agreement for different series of observa- 

 tions. From a comparison of the results for air it seems likely that 

 some unknown disturbing factor is present in water connected per- 

 haps with temperature differences or vortex motion, which produces 

 uncontrolled errors. 



In the fifth column the equivalent length of the pendulum is 



given as determined by oscillating it in air and assuming the value of 



g at Montreal i.e. 980-6. In the sixth column the effective value of 



g is given for each sphere as calculated from its time of swing and 



length 1. 



dv 

 The seventh column contains the value of ~ as calculated from 



a t 



the density and measurements assuming Stoke's law to hold. 



The agreement between the sixth and seventh column is by no 

 means perfect, but it seems remarkable to find it so good. The 

 disagreement is not altogether systematic although the deviations are 

 considerably larger than the accuracy of the measurements. 



Effect of Damping. 



In every case readings of the arc of swing were taken to determine 

 approximately the size of the correction for damping. The magnesium 



