1881.] of some Experiments with Whirled Anemometers. 179 



the preceding tables, are collected in the following table, in which are 

 also inserted the mean errors. 



Anemometer. 



Directions of 

 Rotation. 



High Yelocities. 



Moderate Yelocities. 



Mom. inert, 

 small. 



Mom. inert, 

 large. 



Mom. inert, 

 small. 



Mom. inert, 

 large. 



p. c. 



m. e. 



p. c. 



m. e. 



p. c. 



m. e. 



p. c. 



m. e. 



M 



Opposite .... 



122-6 

 118-4 



2-4 

 2-9 



121 -9 

 117 5 



2 -3 

 2-8 



115-1 

 109-7 



4-9 

 4-5 



113 -2 

 108-5 



5-2 

 5-1 





120-5 



119-7 



112 -4 



110-8 



Adie. 



Alike 



95-1 

 98-0 



2 -3 

 6-5 



94 -2 

 97-3 



2-3 

 6 5 



88 -5 

 82 -6 



4-5 

 7 3 



86 -8 

 81 -0 



5 -0 

 7-3 





96-5 



95-7 



85 -5 



83 -9 



Kraft. 



Alike 



Mean 



101 -5 

 100-8 



2-6 

 1 2 



100-8 

 99-4 



2-5 

 1-3 



89-1 

 87 -8 



4-8 

 5 -0 



86-9 

 86 -0 



5 1 

 6-0 



101 -1 



100-1 



88 -4 



86 -4 



The mean errors exhibited in the above table show no great 

 difference according as we snppose the moment of inertia of the 

 anemometer small or large in correcting for the wind. There appears 

 to be a slight indication, beyond what may be merely casual, that the 

 errors are a little greater on the latter supposition than on the former, 

 which is what we should rather expect ; for an anemometer would get 

 pretty well under way in a fraction of a revolution of the whirling 

 instrument. However, the difference is so small that it will suffice to 

 take the mean of the two as the mean error belonging to the par- 

 ticular anemometer, class of velocity, and character of rotation under 

 consideration. Erom the mean errors we may calculate nearly 

 enough, by the usual formulae, the probable errors of the various 

 mean percentages for rotations opposite and alike. The probable 

 errors of these mean percentages come out as follows : — 



Kew, 1*0 for high velocities ; 2 - 7 for moderate velocities. 

 Adie, 1*5 „ „ 2*0 „ 



Kraft, 0-9 „ „ 1'8 



These probable errors are so small that it appears that for the high 

 and even for the moderate velocities the experiments are extremely 

 trustworthy, except in so far as they may be affected by systematic 

 sources of error. 



If we compare the registered percentages of the true velocity of 



