# Popular Science Monthly/Volume 7/May 1875/Scientific Prophecy

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* SCIENTIFIC PROPHECY.
PROPHECY is the prediction of an event—the declaration of something to come. When future events—either in the history of the world or in the life of man—have been foretold from no known data and from no law, the prophecy must have been divine, for none but God can know the future of man. When such events in the history of Nature and in the life of matter have been predicted from known data and from established laws, the prophecy is human and scientific. Every science in its growth passes through three stages: First, we have the stage of observation, when facts are collected and registered by many minds in many places. Next, we have the stage of ​generalization, when these well-ascertained and carefully-verified facts are arranged methodically, generalized systematically, and classified logically, so as to deduce and elucidate from them the laws that regulate their rule and order. Lastly, we have the stage of prophecy, when these laws are so applied that events can be predicted to occur with unerring accuracy. Astronomy is said to be the only science which has thoroughly reached the last stage. Other sciences are in various stages of growth. Electricity in some branches has reached the third stage, but in many branches it is still in its infantine period. Astronomy predicts eclipses, transits, occultations, for any period in the future, and the "Nautical Almanac" is the most wonderful example of prescient knowledge: a sailor may go away for a five years' cruise, and yet in this book he will find every event in the motion of the planets, the movements of the tides, the rotation of the moon, the eclipses of the sun, etc., faithfully and unerringly foretold. But astronomy has produced greater wonders than these. The planet Uranus was found to suffer from some slight disturbances in her path round the sun. Adams in England and Leverrier in France simultaneously and independently, from the known laws of gravity, predicted the existence and position of another unknown planet. Galle, of Berlin, directed by Leverrier, found the planet in the spot indicated, and it was called Neptune.
Newton, the grandest scientific man the world has perhaps ever seen, and the founder of the laws that led to the prophecy just narrated, in his investigations on light, predicted the fact that the diamond was formed of some combustible material—from its very high index of refraction. The combustion of diamond is now an ordinary, though expensive, lecture experiment. Light has given us one or two other scientific prophecies. Poisson, from theory, pronounced that, in the case of an opaque circular disk, the illumination of the centre of the shadow caused by diffraction at the edge of the disk would be precisely the same if the disk were altogether absent. Arago proved this to be true. Again, Sir William Hamilton predicted that in biaxial crystals there were four points where the refraction of the crystal upon an incident ray produced a continuous conical envelope. Dr. Lloyd took a crystal of aragonite, and, following Hamilton's directions, discovered what the mathematician had predicted.
Whewell predicted from theory that there must be a certain point in the North Sea, midway between Lowestoft and the coast of Holland, where there was no rise or fall of the water, because the crest or high-water mark of the tidal wave, and the trough or low-water mark of the same wawe, reached the same point at the same time, but by different routes. Captain Hewett, R. N., found that it was so.
Electricity has its prophets. Faraday, examining Sir Charles Wheatstone's beautiful experiment on the velocity of electricity by means of a rotating mirror, said: "If the two ends of the wire in ​Prof. Wheatstone's experiments were immediately connected with two large insulated metallic surfaces exposed to the air, so that the primary act of induction—after making the contact for discharge—might be in part removed from the internal portion of the wire at the first instant, and disposed for the moment on its surface jointly with the air and surrounding conductors, then I venture to anticipate that the middle spark would be more retarded than before. And if those two plates were the inner and outer coatings of a large jar or Leyden battery, then the retardation of the spark would be much greater." The experiment was not made for sixteen years. It was then shown as the explanation of the retardation of the current in our subterraneous and submarine wires.
Sir Francis Ronalds, with wonderful prescience, had in 1823—fifteen years before Faraday—suggested "the probability that the electrical induction which would take place in a wire inclosed in glass tubes of many miles in length (the wire acting like the interior coating of a battery) might amount to the retention of a charge, or at least might destroy the suddenness of the discharge." Faraday's prophetic vision and Ronalds's far-sighted knowledge are verified in every working cable. The accuracy with which our cable-repairers are directed by our electricians to the spot where the wire is broken, the exactitude with which the working speed of a cable is predicted, the unfelt and invisible supervision which is exercised over the care and maintenance of our telegraphs—even though they pass through distant countries and different climes—are evidences that electricity, in this particular field, is approaching the last and prophetic stage of its growth. This field is resistance, and Ohm is its prophet.—Telegraphic Journal.