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speed of 5.42 cm of are in the minute. The drum, made 

 of brass and having a diameter of 18.3 cm and a lenglh 

 of 17.2 cm, was overdrawn with paper on which the points 

 through the electromagnet were marked. It was moved by 

 a clockwork and a long screw. Observations showed t hat 

 the speed was so constant that the time could very well be 

 determined by the revolving drum. For every 60 turns of 



:i7 



20 



the anemometer wings, a point was marked on the drum. 

 These points follow a spiral-hne on which the time could 

 be determined, if the starting point was known. 



