COBRESP ONDENCE. 



839 



C BE, ESPONDENCE. 



FLYING. 



Editor Popular Science Monthly : 



I WAS much gratified to see that Dr. Le 

 Conte's very able and interesting article 

 upon flying, in one of your recent numbers, 

 fully recognized the fact that mere air in 

 motion, commonly known as " wind," and pop- 

 ularly supposed to be in most cases moving 

 at a uniform velocity, can not in the long 

 run help a bird or a man to fly. In view of 

 the large amount of foolishness published in 

 the newspapers about rising in the air by the 

 action of the wind, and the strong contrast 

 that is drawn between wind and still air, it 

 would seem probable that the writers in their 

 role of would-be scientists base their doctrine 

 upon the analogy of a rising kite. For the 

 proper " squelching " of these notions their 

 fallacy should be thoroughly exposed, and 

 the real facts set forth as frequently as pos- 

 sible. 



There is no question but that the appar- 

 ent mysteries of rising, soaring, etc., without 

 propulsive action, are due, as has been stated, 

 to variations in air velocity rather than to 

 that velocity itself. These variations can, of 

 course, act only in conjunction with inertia. 

 The bird or other flying machine, drifting 

 with the air at its average speed, takes ad- 

 vantage of the inherent tendency of his 

 mass to maintain its present rate of motion 

 (whether positive or negative or nil in rela- 

 tion to the earth's surface) for a short time 

 after the air velocity has changed, thereby 

 lifting him up by some local body of air 

 with, say, a suddenly increased velocity, act- 

 ing as a wedge beneath the front of his 

 wings (or other aeroplane) while he tem- 

 porarily stays still, or nearly so, in reference 

 to the general body of the air. Should there 

 be a local decrease of velocity the conditions 

 would be equivalent to a "breeze astern," 

 and the rear edge of his wings would have 

 to be elevated at an angle with the plane of 

 the wind's motion that is, if he wished to 

 continue rising. All this is obviously upon 

 the same principle as a block lifted by a 

 wedge slid under it, which can be pushed up 

 so long as it moves forward against the 

 wedge or remains stationary or moves back- 

 ward with the wedge, but at a slower rate of 

 speed. 



If the bird was so fortunate as to be 

 held with the earth against the motion of 

 the wind by a guy- line, after the manner of 

 a kite, or if the block was held from a re- 

 trograding motion by a line in front or by a 

 strut behind it, the matter would of course 

 be perfectly simple ; but it must be strongly 

 impressed upon the popular mind that there is 

 in the case of flying creatures no such holding 



action except that due to inertia, the which 

 can last but a short time. We must there- 

 fore assume frequent changes of air velocity 

 to account for the soaring which we so fre- 

 quently see materialized as an actual fact. 

 Going back to the analogy of the wedge, a 

 very simple experiment will show that the 

 block can be raised much higher by striking 

 the wedge a quick blow, thereby taking a 

 very full advantage of the Inertia of the 

 block, than it can when the wedge is pushed 

 in slowly. If too slowly, its action will of 

 course be nil, and the block will move back 

 with it instead of rising. 



Now it is obvious that we all of us know 

 little enough about the principles of flying, 

 but the first fact to be thoroughly impressed 

 upon the mind of any would-be student of 

 this subject is that wind, regarded usually 

 as air in motion, must be considered as air 

 at rest, and the earth as a moving body slid- 

 ing along underneath it. Of course, this mo- 

 tion of the earth will make a difference to 

 our future flying machines in regard to the 

 time required to get from one place to an- 

 other, according to its direction ; but as far 

 as the operations of propelling, soaring, etc., 

 areconcerned, the idea of wind must be left 

 entirely out of the question except so far as 

 we can learn about and deal with its fre- 

 quent and rapid variations in velocity. It is 

 probable, however, that these are too uncer- 

 tain to depend upon, and our mechanical ef- 

 forts must be directed toward getting any 

 desired motion we wish in a medium of air 

 at rest. The item of wind has therefore, as 

 before stated, nothing whatever to do with 

 the subject except as regards certain diifi- 

 cultiesi in stopping and starting from the 

 surface of the earth and the time, with a 

 given power, requn-ed to traverse given dis- 

 tances thereupon. Oberlin Smith. 

 Bridgeton, N. J., July, 1894. 



A REMONSTRANCE. 



Editor Popular Science Montldy : 



Dear Sir: In your August number it 

 was apparently claimed that the specialty of 

 women, as women, is their power of intui- 

 tion. But what is intuition ? Dictionaries 

 and general usage seem to make the word 

 synonymous with instinct. 



Now it is not so long since it was gen- 

 erally insisted that animals could never rea- 

 son, but acted by instinct only ; and in spite 

 of much talk about " God-given instinct," 

 the talkers actually, and not always secretly, 

 considered their theory as a firm ground for 

 despising animals as unintelligent. 



