156 THE QUANTITATIVE METHOD IN BIOLOGY 



less important errors being continually committed, the effects 

 of the regular increase of pipette B (the effects of growth) are 

 disordered according to the rules of chance. 



The 200 portions may be represented by 200 small dots 

 (Fig. 20), the distance between each dot and a horizontal line ot 

 representing the volume of the corresponding portion. 



Fig. 20 represents the observed growth of the property 

 volume (during a period of 199 x 10 = 1990 minutes) deduced 



] ]l ]]I \V V VI VIJ VIII )X X t 



Fig. 21. — The distance between each small dot and ot is supj)osed to 

 represent the weight of the precipitate in a portion. The thick dots 

 represent the curve o^ growth (see text) ; ol, time ; o, origin 



from the measurement of 200 specimens of successive ages, the 

 last specimen (last small dot) being 199 x 10 = 1990 minutes 

 older than the first one. This total duration may be divided, 

 for instance, into 10 equal intervals, I., II., ... X. For each 

 interval the mean volume of the corresponding specimens (small 

 dots) may be calculated. Since each interval includes twenty 

 specimens, the positive and negative errors are counterbalanc- 

 ing one another in a certain degreed The ten mean values being 

 plotted out in the form of thick dots, it is seen that the latter are 

 situated approximately on a straight hne which is the curve of 



^ The result would be, of course, better if the portions were more numerous. 

 (See, on the conclusion drawn from a series of twenty observations, § 93, p. 1 18.) 



