HIGH FREQUENCY AND HIGH POTENTIAL CURRENTS. 29 ?

or intensity, unless they are very great. Now we can readily con-ceive liow an organism, such as the human, in the eternal processof evolution, or more philosophically speaking, adaptation toNature, being constrained to the use of only the sense of touch orforce, for instance, might develop this sense to such a degree ofsenstiveness or perfection, that it would be capable of distinguish-ing the minutest differences in the temperature of a body evenat some distance, to a hundredth, or thousandth, or millionth partof a degree. Yet, even this apparently impossible performancewould not begin to compare with that of the eye, which is cap-able of distinguishing and conveying to the mind in a singleinstant innumerable peculiarities of the body, be it in form,or color, or other respects. This power of the eye rests upontwo things, namely, the rectilinear propagation of the disturb-ance by which it is effected, and upon its sensitiveness.To say that the eye is sensitive is not saying anything. Comparedwith it, all other organs are monstrously crude. The organ ofsmell which guides a dog on the trail of a deer, the organ of touchor force which guides an insect in its wanderings, the organ ofhearing, which is affected by the slightest disturbances of the air,are sensitive organs, to be sure, but what are they compared withthe human eye! No doubt it responds to the faintest echoes orreverberations of the medium ; no doubt, it brings us tidings fromother worlds, infinitely remote, but in a language we cannot asvet always understand. And why not % Because we live in amedium filled with air and other gases, vapors and a dense massof solid particles flying about. These play an important part inmany phenomena; they fritter away the energy of the vibrationsbefore they can reach the eye ; they too, are the carriers of germs•of destruction, they get into our lungs and other organs, clog upthe channels and imperceptibly, yet inevitably, arrest the streamof life. Could we but do away with all ponderable matter in theline of sight of the telescope, it would reveal to us undreamt ofmarvels. Even the unaided eye, I think, would be capable of dis-tinguishing in the pure medium, small objects at distances meas-ured probably by hundreds or perhaps thousands of miles.

But there is something else about the eye which impresses usstill more than these wonderful features which we observed, view-ing it from the standpoint of a physicist, merely as an opticalinstrument,—something which appeals to us more than its marvel-ous faculty of being directly affected by the vibrations of the