428 Mr. S. K. Cook on the Distrihxdion of 



2. The Method. — The method o£ allowing air-bubbles to 

 ascend or solid spheres to descend in a viscous fluid gives only 

 the total resultant pressure on the sphere, and does not give 

 the distribution of the-pressure over the surface of the sphere. 

 It occurred to the writer while exp.erimenting with spheres 

 in a Kundt-tube that the distribution of pressure around a 

 sphere might be obtained by using a hollow sphere in which 

 there was a small opening, the interior of the sphere being- 

 connected to a manometer. 



3. Apparatus. — A glass sphere of uniform diameter was 

 blown on a capillary tube. At a point in one of the equators 

 of the sphere a small hole was drilled, and it was then 

 mounted in a tube 160 cms. in length and 3*5 cms. in 

 diameter, through wdiich a constant flow of air was maintained. 

 The arrano-ement in oeneral is shown in Plate XYIII. 



fig. 1. 



Great care was taken that all sharp edges which would 

 tend to form surfaces of discontinuity around the opening o 

 (fig. 2) were rounded*. The diameter of the capillary tube c 

 leading to the manometer m {Q.g. 4) was small compared with 

 the diameter of the sphere, being in general less than one- 

 twentieth. The sphere w^as inserted into the tube through an 

 opening in the side, which was so closed that the inner 

 surface of the tube was smooth and continuous. A constant 

 current of air was maintained in the tube by keeping the two 

 ends of the tube at a constant difference of pressure, the 

 end B (fig. 1) being open to the atmosphere w^hile the end A 

 was connected to a mercury manometer 7;i, not shown in the 

 fioure. The air was furnished from a oas-reservoir maintained 

 at constant pressure by means of w^eights. 



4. Methods of Determining the Pressure. — The pressure in 

 the interior of the spheres was determined by w^ater-mano- 

 meters (fig. 4) made from glass of uniform diameter and 

 connected to the sphere through the capillary tube <?, the 

 difference between the levels of the two columns of w^ater 

 being read by a cathetometer reading to 0*1 mm. The 

 manometers were so arranged that the diff'erence between 

 the pressure normal to the inner surface of the tube AB 

 at the point at w^hich the spheres w^ere situated, and the 

 pressure in the sphere could be determined. The difference 

 of pressure between two spheres at any time could also be 

 measured. 



* Von Helmlioltz, " Ueber Discontinuiiiiche FlussigkeitsbeweguDgen," 

 Berl Monatsher. April 1868; Phil. Mag. Nov. 1868. (See Lamb's 

 ' Hydrodynamics,' pp. 100 to 102, reference.) 



