Inventors at Work, with Chapters on Discovery

by George Iles

In addition to separating oxygen from air our vital organs are every moment performing chemical tasks just as elusive. The liver, for instance, is a sugar-maker. The elaboration of living tissue is of transcendent interest to the physiologist; it is fraught with the same attraction to the chemist who would build compounds from their elements, to the engineer who would transform heat or chemical energy into motive power with less than the enormous loss of our present methods.

Flight.

In 1887 the late Professor S. P. Langley of Washington began experiments in mechanical flight. He found that one horse-power will support in calm air and propel at forty-five miles an hour a wing-plane weighing 209 pounds. Dr. A. F. Zahm, of the Catholic University of America, at Washington, has recently ascertained that a thin foot-square gliding plane weighing one pound soars with the least expenditure of power at about 40 miles an hour, while at 80 miles the power required is more than twice as much. As engines have been made weighing less than ten pounds per horse-power, capable of yielding a horse-power for five hours with four pounds of oil, we are plainly approaching the mastery of the air,—so freely exercised by the sparrow and the midge. Among the students eager in this advance are the men who examine with the camera how wings of diverse types behave in flight, and then endeavor to imitate the strongest and swiftest of these wings.

Light.

Professor Langley conducted another inquiry of fascinating interest, this time respecting those natural light-producers, the fireflies, especially the large and brilliant species indigenous to Cuba, Pyrophorus noctilucus. As the result of refined measurements with the spectroscope and the bolometer, the most delicate heat detector known to the laboratory, he said: “The insect spectrum is lacking in rays of red luminosity and presumably in the infra-red rays, usually of relatively great heat, so that it seems probable that we have here light without heat.” When we remember that ordinary artificial light is usually accompanied by fifty to a hundred times as much energy in the form of wasteful and injurious heat, we see the importance of this research. If light can be produced without heat by nature, why not also by art?

Cuban firefly, life size.

Converting Heat Into Work.

Another notable case of efficiency in nature has already been remarked, namely, the conversion by the animal frame of fuel-values into mechanical work. This is of a piece with the chief task of the engineer as he puts his engines in motion by burning coal or wood, oil or gas. It is a remarkably good steam engine which yields as much as one tenth as a working dividend. Gas engines have sprung into wide popularity because they yield larger results, in extremely favorable cases reaching thirty per cent. A heat engine, of any type, has its effectiveness measured by comparing in absolute units the heat which enters it with the heat which remains after its work is done. The zero of the absolute scale is 460° below the zero of Fahrenheit. So that if an engine begins work at 920° Fahr. (1380° absolute), and the working substance is lowered in temperature by its action in the machine until it falls to 460° Fahrenheit (920° absolute), the engine has a gross efficiency of one third. Economy depends upon employing a working substance at the highest feasible temperature in such a mode that it leaves the engine at the lowest temperature possible. Hence we see engineers devising superheaters for their steam, and producing metal surfaces which either need no lubrication at all, or employ such a lubricant as graphite, which bears high temperatures without injury.

Now let us glance at the mechanism of our own frames, which, according to Professor W. O. Atwater, converts about twenty per cent. of the energy value of our food into mechanical work. This is a remarkable performance, especially when we remember that in health the bodily warmth does not rise above 98° Fahrenheit. What explains this amazing effectiveness at a temperature so far below that of either a steam engine or a gas engine? A simple experiment may be illuminating. We take a plate of zinc and a plate of copper; although they seem to be at rest we know them to be in active molecular motion, which motion is set free when they combine with oxygen or other elements. This combination may take place in two quite different ways, which we will now compare. In a glass jar, nearly filled with a solution of sulphuric acid and water, we immerse the plates of zinc and copper without their touching each other; both rise in temperature as they corrode, as they unite with oxygen from the surrounding liquid. We may, if we wish, employ this heat in driving an air engine; but we can do better than that, for an air engine wastes most of the heat supplied to it. We stop the heating process by joining the two plates with a wire through which now passes an electric current, our simple apparatus now forming a common voltaic cell. This current we apply to lift weights, propel a fan, or execute any other task we please, all with scarcely any waste of energy whatever. The instructive point is that now chemical union is taking place without heat, in a mode vastly more economical and easy to manage than if we allowed heat to be generated, and then applied it in an engine to perform work. The conclusion is irresistible: in the animal frame the conversion of molecular energy into muscular motion is by electrical means and no other. When the engineer learns in detail how the task is executed, and imitates it with success; he will escape the tax now imposed on every engine which sets its fuel on fire as the first step in converting latent into actual motion.