58 FRAGMENTS OF SCIENCE. 



Recent experiments have proved that elementary bodies, 

 except under certain anomalous conditions, belong to the 

 class of bad radiators. An atom, vibrating in the ether, 

 resembles a naked tuning-fork vibrating in the air. The 

 amount of motion communicated to the air by the thin 

 prongs is too small to evoke at any distance the sensation 

 of sound. But if we permit the atoms to combine chem- 

 ically and form molecules, the result, in many cases, is an 

 enormous change in the power of radiation. The amount 

 of ethereal disturbance, produced by the combined atoms 

 of a body, may be many thousand times that produced by 

 the same atoms when uncombined. 



The pitch of a musical note depends upon the rapidity 

 of its vibrations, or, in other words, on the length of its 

 waves. Now, the pitch of a note answers to the color of 

 light. Taking a slice of white light from the sun, or from 

 an electric lamp, and causing the light to pass through an 

 arrangement of prisms, it is decomposed. We have the 

 effect obtained by Newton, who first unrolled the solar 

 beam into the splendors of the solar spectrum. At one 

 end of this spectrum we have red light, at the other, vio- 

 let; and between those extremes lie the other prismatic 

 colors. As we advance along the spectrum from the red 

 to the violet, the pitch of the light if I may use the ex- 

 pression heightens, the sensation of violet being pro- 

 duced by a more rapid succession of impulses than that 

 which produces the impression of red. The vibrations of 

 the violet are about twice as rapid as those of the red; in 

 other words, the range of the visible spectrum is about an 

 octave. 



There is no solution of continuity in this spectrum; 

 one color changes into another by insensible gradations. 

 It is as if an infinite number of tuning-forks, of gradually 

 augmenting pitch, were vibrating at the same time. But 

 turning to another spectrum that, namely, obtained from 

 the incandescent vapor of silver you observe that it con- 

 sists of two narrow and intensely luminous green bands. 

 Here it is as if two forks only, of slightly different pitch, 

 were vibrating. The length of the waves which produce 

 this first band is such that 47,460 of them, placed end to 

 end, would fill an inch. The waves which produce the 

 second band are a little shorter; it would take of these 

 47,920 to fill an inch. In the case of the first band, the 



