MEASUREMENT OF LENGTH 



vi. Diameter of a sphere. To measure the diameter of a ball an indirect 

 method must be used, because of the difficulty of measuring the diameter 

 of a sphere directly with a scale. 



FIG. 6. Measurement of the diameter of a sphere. 



Procure two rectangular wooden blocks larger across than the sphere. 

 Push the two blocks against a third, or against any upright surface, so as. 

 to keep them parallel, and then place the wooden sphere between them 

 and measure its diameter, as in Fig. 6. The scale may be placed lying 

 flat on the blocks, and if it is a thin metal rule it can be used in this way. 

 But if a wooden scale is used it should be placed on the blocks " edge on," 



FIG. 7. How to use a scale " edge on " to prevent inaccurate measurement. 



as in Fig. 7. Make measurements with the sphere in different positions,, 

 and find the mean or average result. 



Note. In the previous experiments, each student should take a circle 

 differing in diameter from the others ; so that a set of results can be obtained 

 for circles from, say, one cm. diameter to twenty cms. These results should 

 be collected under the headings of mean diameter and mean circumference.. 

 From the results a graph should be obtained. 



30 



Scale i '= 10 cm. 



20 

 1 



10 



10 15 20 25 30 35 40 45 50 55 60 



Axis of Circumferences 

 FIG. 8. Graph showing the relation between the diameter and circumference of a circle;- 



