430 



TRANSMISSION 



by this amount (9.0 0.171=8.829) and arrive at the true 

 mean 8.83 .* 



Considering next the standard deviation : In column/( V <7) 2 

 we have 548.00 as the sum of the products of the several fre- 

 quencies into their respective deviations from the assumed mean, 

 derived on the same plan as when working from the true mean 



D. Dividing by the total number (327}, we have 548.00 -^-,327 = 

 1.6758, corresponding to the quotient 538.4103 -s- 327 = 1.6465 

 of the previous calculation when working from the true mean. 



The correction made in the mean was o. 171; but as we are 

 now dealing with second powers it seems but natural that this 

 amount should be squared before it can be taken from the quo- 

 tient 1.6758, an operation that can be fully justified by strictly 

 mathematical proof. The square of o. 1 71 is 0.029241, or 0.0292 + . 



* On the other hand, should the sum of the positive deviations exceed the sum 

 of the negative deviations it would indicate that our assumed value is too small, 

 and we should add the correction in order to arrive at the true mean. 



