60 THE ROYAL SOCIETY OF CANADA 



sphere, being the lightest, was damped to the greatest extent. It 

 was found that the correction for this sphere was less than the un- 

 determined errors and hence was not applied. In the heavier spheres 

 the correction was left out of account. 



Conclusion. 



Spheres composed of various metals of densities ranging from 

 11-33 to 1-7 have been oscillated in water. The result has clearly- 

 indicated the general validity of Stoke's^ law which governs the move- 

 ment of such bodies in a fluid medium. 



1 Added October 3rd, 1917— 



Dr. J. C. Glashan has just pointed out to me that the law of the added half 

 mass for spheres moving through a liquid was first given by Poisson in 1831, and that 

 Stokes merely extended the law by adding a correction for the surrounding envelope. 

 However, Chevalier Du Buat in Volume 2 of the second edition of his "Principes 

 d'Hydraulique" Paris 1786, had already announced what was practically Stoke's 

 law, but his experiments gave .585 instead of .5 for the coefficient of the inertia 

 increase due to the fiuid carried by the sphere. As Du Buat 's experiments preceded 

 all other investigations by nearly half a century, it would seem more appropriate 

 to call the law of the added half mass "Du Buat's Law." H. T. B. 



