144 BEES AND BEE-KEEPING. 



support beneath which the centre of gravity, if free 

 to move, always arranges itself. If a ball be held up 

 by a string, the centre of gravity (identical with the 

 centre of the ball, if the latter be of uniform density) 

 comes to rest under the point of support, towards 

 which position it immediately falls after every dis- 

 turbance. If, in flight, a bee desires to rise, she 

 straightens out her abdomen, thus carrying her 

 centre of gravity (or weight) backwards, and, as a 

 consequence, the abdomen, with regard to the rest, 

 sinks, and the head points upwards, the body 

 revolving around the wings, so that the before-men- 

 tioned centre of gravity occupies a position beneath 

 them. This alteration in the direction of the body 

 makes the flight one of ascent. But, on the con- 

 trary, curling the abdomen beneath, by the action 

 of muscles lying in the thorax under the meso- 

 phragma, brings the centre of gravity forwards, and 

 allows the head to relatively sink, and a descent 

 in flight is the result. It is possible that the ab- 

 domen, acting after the manner of a rudder, also 

 occasions, similarly, all lateral changes of direction. 

 It certainly partially effects these movements, but 

 whether assisted by inequality in energy of the rio-ht 

 and left wings, steering as the sculler does, is not 

 yet determined. 



The marvellous velocity with which the wings of 

 most insects vibrate has excited considerable atten- 

 tion, and has been tested by most ingenious experi- 

 ments. 



Let us first refer to what is known as the "Graphic 

 method." A metal drum, revolved by clockwork, is 



