isa-normaladvance-1909-00075

Description:	THE NORMAL ADVANCE75Some explanation of the wTave theory maynot be out of place at this point. The mediumof light is, as you know, the ether. Nothingwill convey radiant energy except this all-pervading, unlimited medium. It is very rare, itsdensity being 9.36 ten-sextillionths (9.36—10,-000,000,000,000,000,000), yet this is enormouslygreat compared with the density that air wouldassume out in interstellar space. It is veryelastic, being 1-100,000,000 as rigid as steel. Itis not made up of molecules or atoms, but ishomogeneous and continuous, structureless,analagous to a jelly. It is gravitationless, being of the same density in all parts of the universe. It is neither heated or lighted by therays passing through it, hence it follows thata point in interstellar space is in absolute darkness and at absolute zero. It is frictionless,isotropic, indestructible and insensible tonerves. And this unique medium is full ofradiant energy, and-as far as is yet known, ofradiant energy alone. This radiant energy isnever at rest but moves through space with auniform, undtilatory motion. When a body isluminous it is so on account of the magneticclutch its molecules have upon the ether andby their magnetic strain or twist they give riseto waves or vibrations that spread in ever-increasing spheres around their source.When it was first conceded that light traveledfrom point to point in space, it was held that itmoved with infinite velocity. In 1675, however, Olaus Romer (Remer), a Danish astronomer, discovered that its speed is finite. Hefound that the interval between the eclipses ofJupiters Satellites is about sixteen and one-half minutes shorter when the earth is in thepoint of its orbit next to that planet, thanwhen in the opposite point. The exact speed oflight, deduced by this method, is, after makingall corrections, and assuming the most probable value of the solar parallix (which is ourdatum for measuring the dimensions of theearths orbit), about 186,500 miles per second.In 1828, James Bradley, an English astronomer, discovered aberration of light. This ismerely the fact that the light of a star doesnot appear to be coming in the proper direction,(unless the earth be moving exactly to or fromthe star), on account of our motion in our patharound the sun, and the finite speed of light.Suppose a raindrop is falling vertically. Ifan observer, with a glass tube, would have thedrop descend axially through the tube withouttouching its sides, he must obviously keep thetube vertical as long as he stands still. Butif he advances he must draw back the bottomof the tube by an amount which equals theadvance he makes while a drop is fallingthrough it. He must incline the tube forwardat an angle, depending upon the velocity of theraindrop and the velocity of his own motion.An additional illustration of aberration isseen in the case of a bullet fired at right anglesthrough the sides of a railway coach. If thecar is at rest, the holes in both sides will be ina straight line with the line of the bullet beforeit entered the coach. But if the carriage be inmotion, the further side of the car will havemoved through a certain space during the interval occupied by the bullet in passing fromside to side, and thus the line joining the holesin the sides will be included at an angle greaterthan a right angle to the direction of the trainsmotion.Thus a star, during a year apparently describes a circular path around its true position.The radius of this circle bears the same ratio tothe stars distance as the speed of the earth doesto that of light. All radii thus examined subtend angles of about 24.47. Hence the speedof light is to the speed of the earth in its orbitas 1: tan 20.47, that is 10,000 :1. The speedof the earth in its orbit is eighteen and one-halfmiles per second. 10,000 times 18y2 miles is185,000 miles, approximately the speed of light.But the first direct measurement of the velocity of light was made by Hippolyte LouisFizeau, a French physicist, by an apparatus asremarkable for its simplicity, as its inventorwas for his ingenuity. Two telescopes wTere setup facing each other, one at the station of theobserver, the other at a distance of 9,440 yards.In the former telescope wras arranged a wheel
Source:	http://indstate.contentdm.oclc.org/cdm/ref/collection/isuarchive/id/34105
Collection:	Indiana State University Archives

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