152 rrulxdth I'Jrror of Sninpluiij lit Soil ,SV//7v//.s- 

 •uul in tlic case of a chemical analysis, 



^n/C3'+(v5/ = ^'^''P'''''^^*- 



Filial |in>lialile error, per cent. 



The table shows that even with 10 borings there is not much diminu- 

 tion in the probable error by taking an a^'erage of two analyses. Since 

 however some check is advisable it is better to make two analyses. 



When two mechanical analyses are peiformed it is seen that not 

 much additional accuracy is obtained by increasing the number of 

 borings beyond six, either in the mechanical or chemical analyses. 

 Taking six as the number of borings the probable error is ± 2-7 per 

 cent. This means that it is an even chance that a result obtained is 

 within 2-7 per cent, of the true result. The chances of a result having 

 lower degrees of accuracy are shown in the following table, calculated 

 from Wood and Stratton's paper on the Interpretation of Experimental 

 results^. 



Percentage deviation 

 from true value 



2-7 per cent. 



3-4 



3-9 



4-6 



51 



5-4 



Chances of result being within 

 limits of such deviation 



Evens 

 3 to 2 



2 to 1 



3 to 1 



4 to 1 

 9 to 2 



1 This Journal, Vol. m. p. 429. 



