WINGS AND FLIGHT. 145 



surrounded by smooth paper, which has been coated, 

 by exposure to a smoky flame, with a thin and easily- 

 removed sooty deposit. If a living insect be so held 

 that the wing in vibrating just touches the paper 

 while the drum is rotating, a series of scratch-like 

 marks, equi-distantly placed [c, d, Fig. 30), will 

 indicate, by the spaces between them, the amount of 

 movement made by the drum during the time occu- 

 pied by each vibration of the wing. This time is 

 accurately determined as follows : A tuning fork, 

 whose note (and, consequently, exact number of vibra- 

 tions per second) is known, has one of its prongs 



Fig. 30.— Graphic Representation of Rate of Vibration of Beit's Wi.no. 

 a, b, Line Made by Tuning Fork ; e, d, Marks Made by Vibrating Wing. 



provided with a small pointed style. The latter, at the 

 moment the insect is being operated upon, is brought 

 into contact with the revolving drum (the fork, of 

 course, sounding), and is so held that the style moves 

 up and down upon the sooty paper. A waved line 

 (like a, b, Fig. 30) is produced, the length of each 

 wave marking the space traversed by the drum while 

 the fork makes one vibration. Should the fork give 

 256 vibrations in a second (sounding the middle C), 

 256 waves will occupy the space moved through by the 

 drum in the same time. If opposite to these should 

 stand 190 dots made by the bee's wing (c, d, Fig. 30), 

 we get 190 vibrations per second as its rate — the 



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