Page:Popular Science Monthly Volume 21.djvu/64

56 We now proceed to the measurements and records that are more especially the subject of this memoir.

Energy may be defined as the length of time during which a person is wont to work at full stretch, day by day, without harm to himself, in obedience to an instinctive craving for work, and endurance may be tested by the same observation if an adequate motive for work be supplied. Some persons seem almost indefatigable; they are never happy or well except when in constant action; and they fidget, fret, and worry themselves under enforced idleness. Others, whose vitality is low, break down under a small amount of strain, and their happiness lies mainly in repose. The true tests would undoubtedly be physiological, and of considerable delicacy, but they have yet to be discovered, or at least to be systematized for anthropometric purposes. They would measure the excess of waste over repair consequent upon any given effort, and would furnish the indications of a loss of capital which, if persevered in, must, infallibly lead to vital bankruptcy. Now, when a haberdasher examines a piece of cloth to learn its strength, he handles and pulls it gently in different directions, but he does not care to tear it to pieces or to strain it. He learns by the way it behaves under a moderate tension how it would support a great deal more of it. So it may prove to be with physiological tests, as applied to the determination of the amount of endurance. The balance of the living system might be artificially disturbed by a definite small force, and its stability under the influence of greater forces might thereby be inferred. Unfortunately, the only convenient tests of a person's endurance that are now available are records of such feats of sustained bodily or mental work as he may have recently performed, that were not succeeded next day by feverish excitement or by fatigue, but whose effects were entirely dissipated by a single night's rest.

The faculties about which I have next to speak admit of being developed in a high degree by exercise, and some difficulty will always arise in knowing how far their development may be due to nature and how far to practice. This difficulty is, however, of less importance than it might appear to be. All our faculties are somewhat exercised in the ordinary course of life, and when we begin to practice any special test, though our skill increases rather quickly at first, its rate of progress soon materially lessens, and we are able to judge with sufficient precision of the highest point which we can hope to attain. When recording the results of any test it would be sufficient to append a brief note concerning the amount of previous practice.

The strength is best measured by a spring dynamometer, of which the framework is held in the left hand with the arm extended, while the spring is drawn back by the right hand in the attitude of an archer. This is the test used by the Anthropometric Committee; it only refers to the strength of the arms, but that is in most cases sufficient to express the general muscular power, and it has the