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 popularly 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 possible.
There is no question but that the apparent 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 advantage of the inherent tendency of his mass to maintain its present rate of motion (whether positive or negative or nil in relation 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, acting as a wedge beneath the front of his wings (or other aëroplane) while he temporarily 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 backward 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 retrograding 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 therefore assume frequent changes of air velocity to account for the soaring which we so frequently 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 sliding along underneath it. Of course, this motion of the earth will make a difference to our future flying machines in regard to the time required to get from one place to another, according to its direction; but as far as the operations of propelling, soaring, etc., are concerned, the idea of wind must be left entirely out of the question except so far as we can learn about and deal with its frequent and rapid variations in velocity. It is probable, however, that these are too uncertain to depend upon, and our mechanical efforts 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 difficulties in stopping and starting from the surface of the earth and the time, with a given power, required to traverse given distances thereupon.
|Bridgeton, N. J., July, 1894.|
Editor Popular Science Monthly:
Dear Sir: In your August number it was apparently claimed that the specialty of women, as women, is their power of intuition. 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 generally insisted that animals could never reason, 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.