Page:Popular Science Monthly Volume 2.djvu/376

360 application of scientific methods. Here we stop, with the sense of a child who has picked up a few spangles which have dropped from Flora's rich attire.



T is a common idea that the saying "as quick as thought" expresses the ne plus ultra of speed—an unapproachable rapidity, instantaneous and lightning-like. The phrase seems used, indeed, as an hyperbole; but in one sense, at least, this is a mistake. Thought, it is true, can transport us afar without taking note of distances, because there is no more difficulty in bringing up, in fancy, a remote object, than one that is close to us, and in this view it may be allowable to say that space creates no obstacle to thought—not impeding nor changing it in the least. But thought never springs instantaneously under the influence of an external cause; an appreciable time elapses, one or two tenths of a second, before an idea is aroused in the mind in consequence of an impression received by the brain, and before it will respond to that idea by the movement of a limb. So the nervous current which transmits sensations to the brain, and bears the commands of the will to the extremities of the body, requires a certain time to finish its course. Impressions coming to us from without are not perceived at the very instant of their production; they travel along the nerves with a speed of from 60 to 90 feet a second, equal to that of the carrier-pigeon, or the hurricane, or of a locomotive under full steam, but very much less than the swiftness of a cannon-ball. For instance, we are conscious of an injury in the feet only after a half-tenth of a second has elapsed. The commands of the will pass from the centre to the circumference with no greater rapidity; the limbs do not instantaneously obey the motive thought. When a movement is provoked by a shock received in any part whatever of the body, the stimulus at first travels as far as the brain; there a thought is developed, the will determines to send out an order; this order runs along the nerves to the limb which is bidden to act, and, at last, the limb begins movement. All this takes place in three times, of quite an appreciable duration.

In the human body, this time lost is a mere trifle, some hundredths of a second; but let us suppose one of a great cetacea, a whale, for instance, in which the telegraphic network of the will controls a wider range. A boat attacks it in the rear, the harpoon strikes the monster's tail. Then the pain sets out on its course to demand revenge; but the journey is long—it must travel over 90 feet before reaching the