# Popular Science Monthly/Volume 34/February 1889/Correspondence

CORRESPONDENCE.

THE FLYING-MACHINE PROBLEM.

Editor Popular Science Monthly:

SIR: To the greater part of Prof. Le Conte's article, "The Problem of a Flying-Machine," in the November number of "The Popular Science Monthly," I give hearty assent, and yet I can not admit that his premises warrant his very discouraging conclusions. lie shows clearly that as the animal, flying or walking, increases in size, the ratio between power and weight grows smaller, until finally the limit of muscular strength is reached; or the "weight over-takes the utmost strength of bones to support or muscles to move." He shows that, among mammals, this limit was probably reached in the gigantic dinosaurs; and that the largest flying-birds, such as the turkey-cock and condor, are "evidently near the limit," and that the ostrich and emu have passed it, and hence arc unable to fly.

He then speaks of the wonderful efficiency of the animal machine as a means for turning heat into work. "Nerve-energy acting through muscular contraction, and supplied by the combustion of foods, such as oils, fats, starch, sugar, and fibrin, together form the most perfect and efficient engine that we know anything of; i. e., will do more work with the same weight of machinery and fuel. ... A bird is an incomparable model of a flying-machine. No machine that we may hope to devise, for the same weight of machine, fuel, and directing brain, is half so effective; and yet this machine, thus perfected through infinite ages by a ruthless process of natural selection, reaches its limit of weight at about fifty pounds. . . . The smallest possible weight of a flying-machine with necessary fuel and engineer even without freight or passengers, could not be less than three or four hundred pounds"; and hence Prof. Le Conte concludes that "since the animal machine is far more effective than any we may hope to make, therefore the limit of weight of a successful flying-machine can not be more than fifty pounds," and that a "true flying-machine, self-raising, self-sustaining, self-propelling, is physically impossible."

Can this be so? Is the animal machine more effective than any we can hope to make? Will it necessarily "do more work with the same weight of machinery and fuel"? Does the limit of weight in a flying animal mark the limit for a flying-machine? At the risk of not being considered "a true scientist" I must decidedly dissent from these views; I can not look upon machine-flight as a real impossibility, similar to the production of perpetual motion or of a self-supporting arch of indefinite length.

Before making a comparison between the power of birds and motors, we must get some idea of the power exerted by the former. How much work must a bird of given weight actually do in order to raise himself from the ground and fly? It is well known that, once in the air, the power required is very much less than that necessary for rising. How much less is uncertain, but in a brisk wind an eagle, or condor, or albatross will circle around for hours, hardly ever flapping his wings, and seemingly the only work is that due to muscular effort in keeping the wings outstretched. The work done in getting up is, then, the greatest the bird or machine would be called upon to do. This work will evidently depend upon the ratio of the wing-surface to the weight; with wings only a square foot in area, the most powerful condor could not fly; and the greater the wing-surface, provided the muscles are strong enough to manage it, the less the power required.

This ratio has been measured on many birds. The vulture, for example, can spread 0·82 of a square foot for each pound of weight, and, assuming the entire weight to be thirty pounds, the total wing-surface would be 24·6 square feet.

We now have a ready means for calculating approximately the maximum power such a bird must be able to exert. In order to rise vertically, he must force the air down-ward until the reaction is equal to his weight. Calling v the velocity of the air in feet per second, R the reaction in pounds, w the weight of a cubic foot of air, A the area of wing-surface in square feet, and g the acceleration due to gravity, we may make use of the well-known formula for reaction: ${\displaystyle \scriptstyle R={\frac {Awv^{2}}{g}}}$ or ${\displaystyle \scriptstyle v={\sqrt {\frac {Rg}{Aw}}}}$ from which substituting values, we find the necessary velocity to be about twenty-three feet per second. The work done in giving the air this velocity would equal ${\displaystyle \scriptstyle {\frac {Rv}{2}}}$, or three hundred and forty-five foot-pounds per second, equivalent to about six tenths of a horse-power. It is here assumed that the air is driven downward in parallel streams; but a bird's wing would naturally send off a part in other directions, and consequently the power necessary would be somewhat greater. Allowing twenty-five per cent for this and other losses, we see that a vulture weighing thirty pounds would not need to exert more than three quarters of a horse-power, and this only for a few moments while rising.

Suppose, now, our flying-machine to weigh six hundred pounds, or twenty times as much, with the same ratio of wing or propelling surface to weight; we should then require simply twenty times more power, or about fifteen horse-power.

There are, I think, few engineers who will assert such a concentration of power impossible, even when the weight of the man, and fuel for a considerable space of time, are included. Indeed, Strongfellow is said to have, years ago, built an engine and boiler complete which gave a third of a horse-power for a weight of twelve pounds, or weighing only at the rate of five hundred and forty pounds for fifteen horsepower.

Prof. Le Conte shows clearly that with birds "the ratio of weight to strength, and therefore the difficulty of rising, increases as the size or weight"; but in a machine it is well known that the above ratio decreases as the weight; or, in other words, we can get a hundred horse-power with a much smaller ratio of weight to power than is possible with a single horse-power.

Even now, using iron and steel and steam, we can concentrate power until we can match the energy of a bird; but, by the substitution of aluminum, possessing equal strength and weighing only a third as much as steel, why should we not hope to do much more than that?

Possibly as a heat-engine the animal machine is more efficient than the best steam-engine, although, nowadays, the "Cornish" can hardly be accepted as a standard of excellence; but it seems to me the problem is one of concentration of power, rather than economy. Surely Prof. Le Conte must be mistaken in thinking we can not equal the birds in this respect. He underrates the capacity of our engineers.

The size of a bird is no doubt limited by the strength of bone and muscle, but we are not confined within anything like such narrow limits. The huge dinosaur had reached Nature's limit of size for a walking-machine; but compare him with man's conception—the locomotive—weighing eighty tons and giving out the power of more than eight hundred horses! The whale appears to mark Nature's limit of size in marine animals. Compare him with our ocean-steamers, indicating fifteen thousand horse-power, and propelled by an instrument vastly more efficient than anything Nature has provided!

Why, then, should we be limited in our flying-machine to the weight or size of the largest bird? Surely, if we can produce in it an equal or greater ratio of power to weight, and can command the use of materials strong enough to stand the strain, we are not restricted as to size.

Nor are we limited in a machine to the birds' way of flying. The leverages of the muscles moving the wings are necessarily short and the strains great, but no more than in a steam-vessel are we bound down by Nature's methods. We may very likely be able, in some ways, to improve on her model.

Even were we to admit Prof. Le Conte's claim that the animal machine can "do more work, with the same weight of machinery and fuel," than anything "we may hope to devise," our engineers need not feel discouraged; for the power required in rising from the ground is manifestly much greater than that necessary for flight, and why should we not be able to take advantage of this by starting from some elevated point, and slide down and up aerial inclines after the manner of a bird? He then apparently does not need do a great deal of work, and why should a properly constructed machine?

The problem is a difficult one, but I can not help thinking Prof. Le Conte at fault in placing its solution among the "impossibles."

 T. W. Mather. New Haven, Conn., December 6, 1888.

DO ANIMALS "PLAY 'POSSUM"?

Editor Popular Science Monthly:

Sir: Walking by a broad ditch, I saw a large, dark-colored snake gliding along the bottom under the water. The creature was coming directly toward me; but as I paused to observe its markings it stopped, raised its head to the surface, and remained motionless. Its back was marked with a pattern of criss-cross curves of pale yellow on a ground-tint precisely like that of water-soaked wood. Presently I began to throw little stones, to make it move on, but it did not stir. Meanwhile, the circles caused by my plashing missiles, the ripple-marks on the sandy bottom, the similar curves on the snake's back, and the crooked, lead-colored neck, all combined to pass off the animal for a water-logged stick. It would have been difficult at that moment to have convinced an inexperienced observer that it was a live snake.

This effect raised the question whether the creature was aware how nearly indistinguishable it had become. It is the common opinion that animals "play 'possum"—i.e., remain passive and apparently helpless under attack—for the purpose of safety, while they are entirely alert and would much prefer to run away. But is this theory credible when we take into account the immense self-control it demands? And can we credit such a seemingly stupid animal as a snake with sufficient intelligence to select deliberately a mode of defense requiring so nice a perception of its own appearance as well as its surroundings? Dr. Abbott thinks that the well-known behavior of the opossum when attacked is due pimply to paralyzing fear, and he supports his theory by many careful observations. If it is true that the opossum faints with terror in the presence of danger, it seems probable that, in the case of other animals, what looks like intelligent dissimulation is really due to helpless fright. If we human folk are sometimes "too scared to move," why not the lower animals also?

 S. F. Goodrich. Geneva, Ohio, September 5, 1888.

INSECT FERTILIZATION OF FLOWERS.

Editor Popular Science Monthly:

I say it is not true that bees work on the same species while on a trip after honey or pollen. I claim much more than this. They work on the flowers of different families. To prove this, go into a garden of flowers during a dearth of nectar and watch the bees go from flower to flower. They will fumble around among the petals of any blossom that contains either pollen or nectar, mechanically and indiscriminately.

 Respectfully yours, Mahala B. Chaddock. Fremont, Ill., November 27, 1888.

WOMAN SUFFRAGE.

Editor Popular Science Monthly:

Mr. Cramer's condensed and categorical criticism in your January issue, of my article on this subject, which appeared in the "Monthly" of last October, deserves a reply from me, since his method is direct, and some of the points he raises will bear further ventilation.

First, as to the physical inability of women to take part in the execution of the laws. This I have thought, in common with many other men, to be a sufficient reason why women are not adapted for taking part in government. We are reminded, in reply, that but a portion of the male sex are required to serve in the army, and none beyond the age of forty-five years in this country; and we are told (not for the first time) that, if we disfranchise on this account, we must deprive of the suffrage our most thoughtful class of voters, our older men. This answer is no doubt an honest one, because its refutation is so easy that it would not be brought forward by any one who can see the situation as it is. The situation is simply this: that in all countries, notwithstanding the forty-five-year limit in this one, men will be called on to do military service, when the case requires it, as long as they can walk and carry a gun. Moreover, it is not chiefly as soldiers that men are liable to do duty in the execution of the laws. Any and all men may be called on by the sheriff of the county to serve as posse comitatus. Moreover, all our civil government rests on the police and judicial system, and not a single one of the preliminary steps in the process can be performed by women. Not a man could be arrested, taken to prison, taken to the court-room, or to punishment, without a male police. Since women can not act in any of these capacities, nor yet as judges, it is evident that the enactment of laws by women, to be executed by men, is government "by women alone." It was in this sense that I used that expression, and not as a question of arithmetic.

Government is in fact the government of men by men. It is men who do things, and, among other things, they are the most frequent law-breakers. It takes men to govern men, and what governs the greater force will control the lesser. It is not necessary to cut two holes in the gate, the one for the large, the other for the small cat. The small cat can go through the large hole.

 E. D. Cope. Philadelphia, December 26, 1888.