368 NEWTON S PRINCIPIA. 



The suspension of clouds may, therefore, be explained 

 according to this theory. The minute drops are really 

 falling with very small velocities. 



The investigations for the motion of cylinders have also 

 been effected, but it will detain us too long to consider all 

 the results. One fact in connexion with the cylinder is 

 remarkable. The motion of the fluid in immediate contact 

 of a sphere moving in a fluid is the same as that of the 

 sphere, and as we go from the surface into the depths of 

 the fluid, the velocity differs more and more from that of 

 the sphere, and finally ends in being zero. The sphere by 

 the friction of its surface tends continually to increase 

 the mass of fluid it drags with it; the friction of the fluid 

 at a distance tends continually to diminish it. These two 

 in the case of a sphere tend to equality, and the motion is 

 ultimately uniform. Not so in the case of a cylinder: the 

 increase on the quantity of fluid carried gains on the de 

 crease due to the friction of the fluid, and the quantity 

 carried increases continually. The velocity must therefore 

 decrease continually. 



Professor Stokes has also submitted his results to a 

 comparison with experiment. He first proceeds to obtain 

 l*S, the only constant at his disposal : the results of Baily 

 with cylindrical rods give 



VJT =-116. 



&quot; It is to be remembered that V]j/ expresses a length di 

 vided by the square root of a time, and the numerical 

 value above given is adapted to an English inch as the 

 unit of length, and a second of mean solar time as the 

 unit of time.&quot; 



Let us take one instance of his series of comparisons at 

 random : let them be the experiments of Baily on spheres 

 attached to fine wires. Allowance is made for the wire by 

 the theory of the motion of a cylinder. Allowance is 

 also made for the confined space, which is estimated as 



