SPECTRUM ANALYSIS 



SPEEDOMETER 



,ment has shown that when the light of a glow- 

 ing substance is passed through the vapor of 

 another substance, this vapor absorbs the col- 

 ors that appear in the spectrum of the absorb- 

 ing substance, causing black lines to appear in 

 the spectrum. A spectrum formed in this way 

 is called an absorption spectrum. To illustrate, 

 the interior of the sun is a glowing mass, but 

 when viewed through the spectroscope, the 



SPECTRUM ANALYSIS 

 (v) Violet (i/) Yellow 



(t) Indigo 



(o) Orange 

 (r) Red 



(6) Blue 

 (g) Green 



solar spectrum contains a number of dark lines 

 which are caused by gases that surround the 

 heated interior of the sun and absorb the colors 

 that they produce in the spectrum. 



Fraunhofer Lines. The different colors of 

 each substance always appear at the same place 

 in the spectra. Consequently, when a dark line 

 appears in place of the color that a given sub- 

 stance, as sodium, would produce, it proves 

 that the light from the substance under ob- 

 servation is passing through the vapor of so- 

 dium. These dark lines were discovered by 

 Fraunhofer, a Bavarian optician, and in honor 

 of their discoverer were named Fraunhofer 

 lines. The German physicist Kirchhoff con- 

 cluded that these lines were caused by the 

 presence in the sun's atmosphere of those sub- 

 stances which themselves produce bright lines 

 in the same position on the spectrum. That 

 is, the spectrum revealed the substances of 

 which the sun was composed. Further experi- 

 ments showed the planets, including the earth, 

 and the stars to be composed of the same sub- 

 stances. Concerning the importance of this dis- 

 covery the eminent scientist Helmholtz said: 



It has excited the admiration and stimulated 

 the fancy of men as hardly any other discovery 

 has done, because it has permitted an insight 

 into worlds that seemed forever veiled to us. 



344 



Uses. Spectrum analysis is employed in 

 testing minerals for the discovery of new met- 

 als, and a number of rare metals, such as 

 helium, have been discovered in this way. It 

 is also employed in testing the purity of sub- 

 stances, since the minutest quantity of an adul- 

 terant can be detected. It is estimated that 

 the spectroscope will detect the presence of as 

 small a quantity as ssirJwff f a grain of 

 lithium. 



Related Subjects. The reader is referred to 

 the following articles In these volumes : 

 Light, subhead The Rainbow 



Spectrum Spectroscope 



SPEECH, the production by the vocal or- 

 gans of articulate sounds for the purpose of 

 communicating ideas. In a sense it means the 

 same as language, but more accurately con- 

 sidered, the latter is the organized body of 

 articulate sounds, while speech is the art of 

 producing those sounds. Besides man, no ani- 

 mal so far as is known is capable of anything 

 which may be correctly termed speech, but 

 certain birds may be trained to imitate very 

 closely the sounds produced by the human 

 voice. Just how many sounds and modifica- 

 tions of sounds are used in the speech of man- 

 kind is not known, but scholars estimate them 

 at approximately 1,000 in the 3,400 languages 

 and dialects of the world. Since the vocal or- 

 gans differ in their formation or development, 

 sounds easy and natural to one body of people 

 may be practically impossible to another, and 

 few if any languages contain over fifty distinct 

 sounds. See LANGUAGES OF THE WORLD. 



SPEEDOMETER, speed om ' e t er, or CY- 

 CLOMETER, siklom'eter, a mechanical de- 

 vice attached to the wheel of a vehicle, indi- 

 cating the distance traveled. In reality the 

 speedometer and cyclometer, the uses of which 

 are practically confined to bicycles and auto- 

 mobiles, are two different instruments, but they 

 are closely connected in principle. The cy- 

 clometer, by a system of clockwork, set in 

 operation by a cam on the spoke of a wheel, 

 indicates the distance traversed. The speed- 

 ometer has an extra attachment which causes 

 the rate of speed, in miles per hour, also to 

 be indicated on a dial. 



A similar instrument is used by surveyors, 

 and is attached to the wheel of a light vehicle, 

 or to a wheel with a shaft or handle by which 

 it is pushed along, each revolution causing 

 clockwork to be set in motion. The number 

 of revolutions is indicated on a dial, and from 

 this, knowing the circumference of the wheel, 



