230 PHENOMENA OF FLIGHT IN THE ANIMAL KINGDOM. 



The elementary psycliical action which we have examined has not yet 

 attained the greatest degree of simplicity. Since, in the solution of the 

 preceding dilemmas, two operations of the brain can be distinguished — 

 first, the distinction between different impressions ; second, the volition of 

 an act chosen from among other acts — Bonders asked himself if it might 

 not be possible to determine separately the time appertaining to each of 

 these two terms. The following is the experiment which he instituted 

 to attain this object : 



First case. — An observer was warned that a vowel would be pro- 

 nounced, and was directed to reproduce the sound heard. 



Second case. — The observer in this second arrangement was directed 

 to respond only to a single vowel — i,for example — and to keep silence for 

 all others pronounced. His effort Avas then entirely directed toward the 

 recognition of t, the vocal organs were placed in the proper position, and 

 the impulse of the breath alone was needed to emit the corresponding 

 sound. We readily comprehend how much the second term of the psy- 

 chical action is simplified under these conditions. The will having only 

 to apply itself to the production of such a sound, rather than any other, 

 reacts, so to speak, without a previous judgment, and the signal follows 

 the act of volition as simply as can be imagined. We naturally observe 

 that this restricted operation occupies less time than the first by the 

 amount of time necessary to respond to each sound with its equivalent, 

 and this difference corresponds to the action no longer required by the 

 brain. 



The preceding considerations indicate sufficiently the path which Ave 

 have to follow. Having to study the function of aerial locomotion, we 

 shall examine the organ which serves to accomplish it, namely, the 

 wing. It is by the movements of their wings that animals sustain and 

 direct themselves in the air. They strike the atmosphere Avith repeated 

 blows, and the reaction of this fluid on the surface which they expose 

 serves for the ijropulsion of the entire body. 



I. — Flight of insects. 



The first subject which presents itself for our investigation will be 

 the inquiry as to the frequency of the motions of the wings of in- 

 sects. Here we encounter the first difficulty. The moA'ements of the 

 wings are so rapid in most cases that the eye cannot count or follow 

 them. There are A^ery few insects which fly slowly enough to render 

 this direct determination possible. Among the most common we may 

 mention the white butterfly which is frequently met with in our fields, 

 the cabbage Pieris. This insect, which has a jerking flight, seldom exe- 

 cutes more than eight or nine moA^ements of the wing in a second; Avhile 

 those insects Avhose flight is directed with precision and without jerks 

 toward a tletermined point generally execute hundreds of strokes of 

 the wing in a second. Thus, in the majority of cases, direct observa- 

 tion cannot folloAV the wing of insects. We obserA'e a body in motion, 

 but we only perceiA^e the extreme limits of its oscillation ; it may, how- 

 ever, be said that these limits are seen with great precision. But 

 that observation may be facilitated, it is necessary that the subject of it 

 shall be placed in a faA^orable situation. We take, for example, one of 

 those Macroglossa (sphynx moths) which frequently serve as the subject 

 of experiments on account of their large size and the readiness with 

 which they are obtained. Fastening its body Avith a pin between two 

 strips of cork in such a way that it shall not turn around upon the 

 axis which pierces it, and that the motion of its wings alone shall be en- 



