Measurement of Area and Volume 41 



reading must be taken at the lowest point of this curved 

 surface, which is called the "meniscus". Should the 

 lower edge of the meniscus not be sharply defined, 

 a white card should be held obliquely behind the 

 cylinder, with its lower edge just below the meniscus, 

 when the -latter will stand out sharply (see Fig. 17). 

 The reading as shown in the figure is 547 c.c., the 

 units figure being estimated by imagining each scale- 

 division to be further divided into 10 equal parts, 

 each representing I c.c. 



Drop a lump of coal or other irregularly- shaped 

 solid object which must be made of material imper- 

 vious to, denser than, and not acted upon by, water 

 into the cylinder. The level of the water will rise and, 

 after ascertaining that no air-bubbles are clinging to 

 the immersed body, take the reading at the new level. 

 Suppose this to be 682 c.c. It is evident that the 

 solid has displaced a bulk of water equal to its own 

 and that its volume is consequently (682 547)= 135 c.c. 



In the case of solids acted upon by water, a similar 

 method of finding the volume may be employed, sub- 

 stituting for water a liquid which does not affect the 

 solid. 



EXPERIMENT 12. Find the volume of a large lump 

 of crystallised copper sulphate (bluestone or blue 

 vitriol) by the method of the previous experiment, 

 using paraffin oil instead of water. 



A further method of determining indirectly the 

 volume of a solid body is described in Chapter vi. 



