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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



under the influence of attractions and repulsions, 

 there can be no initial impulse which is not in- 

 stantly met by resistance, no motion therefore 

 which does not partake of the wave character. 



An initial impulse, if unresisted, would, it is 

 supposed, continue with unvarying velocity and 

 direction through space and time forever. But 

 by the action of surrounding resistances, which 

 are themselves perhaps but modifications of other 

 initial impulses, its equilibrium is upset, its ve- 

 locities made inconstant, its direction and inten- 

 sity altered, divided, scattered, or concentrated, 

 in a thousand different ways. How the initial 

 impulses originated we need not inquire. We 

 have to deal with a universe in which they have 

 been operating practically for infinite time, and 

 to estimate as accurately as we can their present 

 condition. 



It seems correct to speak of these impulses as 

 separate and individual phenomena, because, al- 

 though the whole force of the universe is proba- 

 bly a unity, it presents itself to our senses and 

 understandings as divided everywhere into dis- 

 tinct units. In their simplest form we conceive 

 of these units of force as associated with material 

 " atoms." 



Wherever heat exists the material atoms are 

 supposed to be in a state of perpetual agitation, 

 and every minute atomic movement originates a 

 " wave " of force in its simplest character, the 

 differences between such an atomic wave and the 

 great secular waves with which astronomy and 

 geology mainly deal being probably differences 

 due to increased intensity and complexity alone. 



The normal life of a wave dates from the 

 starting-point of its initial impulse to its maxi- 

 mum of compression or retardation, and thence 

 through the period of reaction till it returns to 

 its original condition. But in vast numbers of 

 cases this normal life is not completely fulfilled. 

 The surrounding conditions being continually 

 varied, in a succession of similar impulses, no 

 two will meet precisely the same fate. Many of 

 them will be checked at different periods of their 

 career, absorbed, divided, repelled, turned aside, 

 or compounded with others ; and out of this 

 complex action new impulses will arise to pass 

 through similar changes, and so keep up the per- 

 petual agitation and life of the material uni- 

 verse. 



The forms of wave-motion may be indefinite- 

 ly varied, but the three leading types are — (a) 

 the wave of oscillation ; (b) the wave of undula- 

 tion ; (c) the centripetal wave ; the wave of os- 

 cillation being represented by the simplest atomic 



movement, while all compound movements tend 

 toward the undulatory or the centripetal forms. 



A simple atomic vibration, in a molecule of 

 unstable composition, may be followed by mo- 

 lecular change and recomposition, the effects of 

 which are passed on through surrounding matter 

 in a succession of compound waves. These com- 

 pound waves, meeting everywhere with other 

 compound waves of varied form and intensity, 

 may either be dissipated early in their career, or 

 may pass through their normal life, or may be 

 taken up without dissipation into the life of an- 

 other compound wave of greater intensity or 

 wider scope. By this latter process of absorp- 

 tion, combined with the reverse process of sub- 

 division, a wave of great initial intensity may be- 

 come complex to a degree scarcely conceivable 

 by the human understanding. 



From atomic vibration to a solar system is a 

 long leap, but it is no more than the result of 

 such composition of wave-motion carried on 

 through indefinite time. 



From a solar system to an acorn is a long 

 leap also, yet it is probable that this, too, is only 

 a result of the same law, only a still further de- 

 velopment of the complexity of wave-motion. 

 An organic unit seems to be the latest outcome 

 of compounded force— the most complex form 

 of wave yet attained to, in at least this corner of 

 the universe. 



If we examine the structure of a complex 

 wave, we find that it consists of an organized 

 body of waves, arranged after the manner of a 

 disciplined army. There is first a single inclu- 

 sive impulse, of the highest intensity and widest 

 scope, holding in its grasp the total body of sub- 

 sidiary waves, and representing the general in 

 command. Then there are a few large, well- 

 marked, secondary impulses, like separate bri- 

 gades, working toward special goals, but with a 

 common end in view. Each of these secondary 

 waves is made up of a number of tertiary waves, 

 which may stand for regiments, and within each 

 regiment are again companies, squads, and finally 

 individuals, the number of component waves in- 

 creasing with each step downward. But this or- 

 ganized arrangement of a crowd of units is not 

 the only kind of complexity to be considered. 

 Besides having its definite place in the system, 

 each subsidiary wave has also its own normal 

 period of life, and its own velocity, which varies 

 not only in its totality, but in its two phases, viz., 

 the ascending phase, in which it approaches tow- 

 ard its climax, and the descending phase, in 

 which it recedes from it. These phases may 



