Shbehy — Average Percentage of Fat in a Coivs Milk. 553 



The averages 

 follows : — 

 June 24 to July 29, 

 ,, 25 ,, 30, 



of six samples taken at seven-day intervals are as 



3-81 

 4-16 



June 26 to July 31, 

 ,, 27 to Aug. 1, 



3-51 

 4-03 



Assuming that a figure departing by not more than 10 per cent, from the 

 calculated average would be satisfactory — that is that the result in this case 

 should be not less than 3'47 per cent., and not greater than 4 - 25 — any 

 of the above would, in the majority of cases, give a fair approximation. 

 Sometimes, however, the result is outside the limits of error (averages 

 outside limits of error are marked thus *) ; and, therefore, samples taken in 

 this Way are not always to be relied on. Four samples are not sufficient, 

 but as the number of samples is increased the result becomes more reliable. 



Can an equally or more satisfactory result be got by any less laborious 

 method ? A glance at an imaginary smoothed-out curve of fat percentage 

 rising gradually during the period in diagrams II and III shows that the 

 curve approximates to the true average for the whole period near its centre, 

 say from July 7th to July 21st. It will be noticed also that a large 

 fluctuation above or below the smoothed curve is usually compensated by a 

 fluctuation in the opposite direction immediately afterwards. It is, therefore, 

 suggested that a good approximation might be got from samples taken on 

 two or preferably four consecutive days near the middle of the period. For 

 cow 97 the following are the averages of some four-successive-day tests: — 



July 



4s 



