THE HOVER-FLY 89 



ethereal, the wings and body of the creature 

 are material, and therefore should be open to 

 investigation. 



Thus, we will suppose that the wings of the 

 hover-fly, Uke all other wings, move with a 

 straight up-and-down action ; but, in this 

 case, they move at the rate of, say, 400 

 vibrations per second (a low computation). 

 Enormous energy is thus developed ; but the 

 fly has such perfect control over it that, whilst 

 careering at infinite speed, it can check itself 

 instantly and remain stationary in mid-air 

 with the engines, so to speak, still running at 

 high pressure. 



When so stationed in mid-air, the insect's 

 body is on the mean level, therefore there is 

 no Ufting force. But in the ordinary course 

 the insect in this position should be driven or 

 " fanned " along in a forward direction ; but 

 it is not, it remains stationary ; because, I 

 beheve, the motive power has been neutraUzed 

 by a slight alteration from the normal in the 

 position of the wings. That is to say, the wing- 

 points are directed slightly forwards, which 

 causes the air to flow off laterally instead of in 

 the rear of the body ; forward tendency is 

 thus counteracted, and consequently the 

 insect hovers in a neutral position, moving 

 neither backwards nor forwards. But the 



