514 



To use this R has to be measured at a number of angles giving equally spaced values of cos 6 

 and the product RP^ (cos &) then integrated nunerically. This method has the advantage that any 

 co-efficient is given without assuming that any of the others are zero. The rain disadvantage is 

 that because of the fluctuations of P (cos (9) over the range the nunOer of radii which must be 

 measured to give any reasonable accuracy in the nunerical integration is rather large. This point 

 is brought out in the following table in which the result of analysing the shape shown in Figure 6 

 by the two methods is compared. Simpson's rule was used for the numerical integration, and 9, n 

 and 21 ordinates were measured. 



Comp arison cf Methods of Shape Analysis 



The table shows that the 7 ordinate method using equation (3) is quite adequate, at least 

 up to 0^. and clearly involves only a third of the labour of the method using equation (4) and 21 

 radii vectores. 



