isa-normaladvance-1909-00074

Description:	74THE NORMAL ADVANCESCIENCE DEPARTMENTThe Speed of LightIt has been reported that upon one occasiona certain high school student in his Freshmanyear was asked this question in an examination: How has the velocity of light beenmeasured? The following is his reply: Anatheistic scientist (falselyso-called) tried experiments on the satellites of Jupiter. He foundthat he could delay the eclipse sixteen minutesby going to the other side of the earths orbit in fact, he found he could make the eclipse happen when he liked by simply shifting his position. Finding that credit was given him fordetermining the velocity of light, by this means,he repeated it so often that the calendar beganto get seriously wrong and there were riots,and Pope Gregory had to set things right.While it would be an interesting psychologicalstudy to determine the mental process by whichthe youth arrived at his idea of a scientistroaming at will over the interstellar space, it ismore to our purpose at present to discover thetruth about the speed of light, and the methodsby which the same has been measured. So weare off for our second lay excursion into therealm of science.According to the first theory of light, ofwhich we have any account, it had no speed,for it did not travel. A strange theory that!How could men see, say the sun, unless the lighttravels from the sun to the earth? A simplematter, said the scientists of the fourth century, B. C, there are very fine, long, invisibleprojections that reach from the eye up to thesun and are affected by the light, and this touchcomes down the tentacles to the eye, and thuswe see. Truly, this was a very simple explanation of the matter.At a much later day the scientists enrolledthe Emission of Corpuscular Theory. Thistheory has it that light consists of infinitelysmall and highly elastic particles, propelledfrom the original huninous source with an inconceivable speed. The particles or corpusclescoming in contact with the retina were supposed to produce the sensation of vision. Thegreat Newton elaborated this theory, and explained rectilinear propagation, reflection andrefraction by its use.But new optical problems arose which required new explanations, and each new explanation required a new hypothesis until mengrew out of patience with a theory that wouldnot explain phenomena and at last Arago, aFrench physicist, gave it a final puncture, witha crucial experiment, and the Emission Theorycollapsed. One main objection to the hypothesis wTas that the momentum that the corpuscleswTould gain in traveling through space at suchan enormous velocity, would, in their impactwith the retina, produce an effect that humannerves could not withstand. Another objectionis the fact that light itself is invisible, whichwould not be true if the Corpuscular Theorywere correct. Moreover Fizeau and Faucaultproved that the velocity of light in water is lessthan in air, and this demonstration helped inthe overthrow of the unpopular hypothesis.The Undulatory Theory is the one now generally accepted. Its characteristic quality is, asthe name implies, wave motion. All phenomena of light, colors, absorption, reflection,refraction, etc., may here find satisfactory explanation. Not only does it seem to explain thephenomena of light, but it is generally conceded by the foremost thinkers of today, thatthe wave theory will ultimately lead to acommon explanation of the phenomena ofchemistry, optics, spectrum analysis, heat radiation and radio-activity.
Source:	http://indstate.contentdm.oclc.org/cdm/ref/collection/isuarchive/id/34104
Collection:	Indiana State University Archives

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