390 



Journal of Agricultural Research 



Vol. IV, No. s 



group h; 95 per cent of the time that group a is at least 19,250 dgm. 

 per sq. mm. stronger than group h; 99 per cent of the time that group a 

 is at least 15,700 dgm. per sq. mm. stronger than group h\ 99.9 per cent 

 of the time that group a is at least 13,500 dgm. per sq. mm. stronger than 

 group h and 99.99 per cent of the time that group a is at least 1 1,000 dgm. 

 per sq. mm. stronger than group h. We thus read immediately the 

 degree of accuracy to which any measurement is entitled. 



As a further illustration, a series of tests were taken on the breaking 

 stresses, diameters, tensile strengths, Young's moduli, and elastic limits 

 of the fibers of samples of wool clipped from the same sheep in successive 

 years, to determine the effect of the age of the sheep on the wool. Taking 

 two of these elements — namely, the breaking stress and elastic limit — 

 it may be shown how accurately we may state the probable tendency 

 of change from year to year (Table IV). 



Table IV. — Probable change in the breaking stress and the elastic limit of fibers of wool 



" Increase. 



Table shows that in case of the breaking stress the chances are 

 approximately 2 to i and 3 to i that there was a decrease in the breaking 

 stress from the first to the second and from the second to the third year, 

 respectively, and does not permit us to make a decided statement that 

 there was a decrease those two years. On the other hand, the chances are 

 better than 10,000 to i that from the third to the fourth year and from the 

 fifth to the sixth year there was a decrease as well as from the fourth to 

 the fifth there was an increase in breaking stress. Likewise, we are 

 practically certain that there was a decrease in tensile strength from the 

 second to the third and from the fifth to the sixth years, while in the case 

 of other years the probability is not great enough to justify any very 

 decided statement. 



