C. B. WARRING. 73 



bottom would evidently acquire a certain horizontal* mo- 

 tion, one to the right, the other to the left. If now the 

 tee-square be quickly turned over, so that the top and 

 bottom change places, this will not interfere with mo- 

 tion previously acquired. The bottom (which has now 

 become the top) will continue to move to the left, while 

 that which a moment before was the top will move to 

 the right, and, as the motion continues (as in case of a 

 pendulum) the ends of the cross are pushed back to 

 where they were, and the instrument rises to its first po- 

 sition. So long as this continues the instrument will 

 maintain its position, or at least it would if the change 

 were instantaneous. As it is not, it falls slowdy. 



This answers the first question. 



Second. Why does the instrument rotate around the 

 central point, in a direction always the opposite of that 

 of the disk % 



Take the tee-square again. Let it fall again a few 

 inches. As in the first experiment, the top, when the 

 tee goes down, gets a motion towards the right — (if held 

 as before) — but, before the instrument can be reversed, 

 it must go half way, and point, instead of up and down, 

 horizontally. Evidently the motion which sends the 

 upper end to the right, will push the instrument (if the 

 top Avas revolved towards the south) toward the north. 

 Hence we have the horizontal motion. 



Another question naturally suggests itself. Why, it 

 may be asked, is the horizontal motion slow in propor- 

 tion as that of the disk is rapid % 



All depends upon the movement of the arms of the tee. 

 If this turns slowly, it has more time to give motion to 

 the ends of its arms, consequently they push it around 

 faster. If the tee turns very quickly, it falls a very 

 short distance, (has so little time), hence the ends of the 

 arms get very little motion, and, of course, can impart 

 but little. Hence a quick motion of the disk makes a 



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