223 



Determination of the time. 



The time, which the drum iised for 10 full tiirns, was 



observed on a Chronometer as follows: 



1:0 V 46"^ 4^ ] 



2:o V' 46"! 2« I the mean l^^ 46'^ 3.7« 



3:o V' 46'ii 5« J 



The constancy of the speed must be regarded as satis- 

 factory for the determination of time by equidistant points 

 on the drum. 



Determination of the velocity of wind in meters per second. 



If r signifies the mean velocity of wind in "Vsec during 

 an interval of 13 sec, n the number of turns of the ane- 

 mometer divided with 60, viz the registered number of tums 

 of the toothed wheel in the same interval of 15% and fmally 

 a and h constants, w^e will have. 



v = a -f- f> n 



The constants were determined' in two different ways 

 with a centrifugal apparatus. The anemometer was fixed 

 in the end of a horizontal narrow board, the other end of 

 which was attached on the vertical axis of the apparatus. 

 The distance between the axis and the anemometer was 



in the first case • • 1.5 1 m 



and in the second 3.0 2 m 



An assistant put the centrifugal apparatus in motion and 

 gave a sign when the speed, regulated after a metronom, 

 was constant. The observer closed the current of the re- 

 gistering apparatus in the moment a sound marked the be- 

 ginning of a revolution. In the same moment he iioticed 

 the Chronometer and, continuing to count the revolutions, 

 he interrupted the current just as the tenth had passed, 

 noting afresh the Chronometer. During this interval a num- 

 ber of points was printed on the drum by the registering 

 apparatus. 



