206 ANIMAL MIX'IIAMSM. 



very nearly horizontal; in the hymenoptera, tlie wing moves 

 in a plane of nearly 45, but vhe lepidoptera flap their wings 

 almost vertically, after the manner of birds. 



In order to render the influence of the plane of oscilla- 

 tion more evident, and to show that the force derived from the 

 resistance of the air has the double effect of raising the in-< i-r 

 and directing its course, we must arrange t\\e ji'ujht intd-min-nt 

 in a peculiar manner. It, will be necessary, in the first place, 

 to be able to change the plane of oscillation of the wings, 

 winch is effected by placing the drum on a pivot at the ex- 

 tremity of the horizontal tube, at the end of which it turns. 

 To show the ascensional force which is developed in this new 

 arrangement, the instrument must no longer be confined to a 

 simple movement of rotation in the horizontal piano, but it 

 must be able to oscillate in a vertical plane like the scale beam 

 of a balance. 



Fig. 88 shows the new arrangement which we have given 

 to the instrument in order to obtain this double result. 



In this modification of the apparatus, the air-pump which 

 constitutes the moving force is retained ; as is also the turn- 

 ing 1 column which moves in the mercurial gasometer. But 

 above the disc which terminates this column at the upper end, 

 is fixed a new joint, which allows the horizontully-bulauced 

 tube at the end of which the artificial insect is placed, to 

 oscillate in the vertical plane like a scale-beam. In order to 

 establish a communication between the revolving column and 

 the tube carrying the insect, we make use of a little india- 

 rubber tube, sufficiently flexible not to interfere with the 

 oscillatory movements of the apparatus. 



Oilier accessory modifications may be seen in fig. 88; one 

 consists in employing a glass tube to convey the air from the 

 pump which moves the in>i t ; ; the other in a change of the 

 in-': lianism by which motion is imparted to the win^s. The 

 most important alteration is the introduction of a joint \\hieh 

 allows us to give every possible, inclination to the plane in 

 \\ hivh the \\ ings oscillate. 



The apparalus bring arranged so that the counterpoise, 

 having he"ii brought nearer to the point of suspension, does 

 l:ot ixactly balance the weight of the insect, the latter is 



