Wave-motion 

 Weaving 



SCIENTIFIC SIDE-LIGHTS 



750 



of the succeeding wave, rise again until they 

 reach the crest, and then sink as before. 

 Thus, while the waves pass onward horizon- 

 tally, the individual particles are simply 

 lifted up and down vertically. Observe a 

 sea-fowl, or, if you are a swimmer, abandon 

 yourself to the action of the waves; you are 

 not carried forward, but simply rocked up 

 and down. The propagation of a wave is the 

 propagation of a form, and not the trans- 

 ference of the substance which constitutes 

 the wave. TYNDALL Lectures on Light, lect. 

 2, p. 52. (A., 1898.) 



3713. WAVES HEAVING EARTH'S 

 CRUST IN EARTHQUAKE Trees Lashing 

 Ground with Their Branches. The whole of 

 the country over which the effects of the 

 great shocks [of the Calabrian earthquake] 

 extended was at times heaved simultaneous- 

 ly, like an angry sea, and sensations resem- 

 bling seasickness were experienced by many 

 of the inhabitants. Those who have watched 

 the sky from the deck of a sea-tossed ship 

 will have noticed that the drifting clouds 

 seem at times to be arrested in their mo- 

 tion; it is in reality the ship which is mov- 

 ing for the moment in the same direction as 

 the clouds, and thus neutralizes the effects 

 of their motion. The same phenomenon w r as 

 observed during the Calabrian earthquake; 

 and nothing serves to give us a stronger 

 impression of the turbulence of those inter- 

 nal heavings which make the dry land as 

 unstable as the billows of a swelling sea. 

 Trees whose roots continued firmly embedded 

 in the soil were seen to lash the ground with 

 their branches. PROCTOR Notes on Earth- 

 quakes, p. 3. (Hum., 1887.) 



3714. WAVES, INTERFERENCE OF 



The Whirlpool at Niagara Motion 

 Doubled or Annulled. The first impression, 

 and, indeed, the current explanation of these 

 rapids [of Niagara] is, that the central bed 

 of the river is cumbered with large boulders, 

 and that the jostling, tossing, and wild leap- 

 ing of the water there are due to its impact 

 against these obstacles. A very different 

 explanation occurred to me upon the spot. 

 Boulders derived from the adjacent cliffs 

 visibly cumber the sides of the river. 

 Against these the water rises and sinks 

 rhythmically, but violently, large waves 

 being thus produced. On the generation 

 of each wave there is an immediate com- 

 pounding of the wave-motion with the river- 

 motion. The ridges, which in still water 

 would proceed in circular curves round the 

 center of disturbance, cross the river oblique- 

 ly, and the result is that at the center waves 

 commingle which have really been genera- 

 ted at the sides. This crossing of waves 

 may be seen on a small scale in any gutter 

 after rain; it may also be seen on sim- 

 ply pouring water from a wide-lipped jug. 

 Where crest and furrow cross each other the 

 wave is annulled; where furrow and furrow 

 cross, the river is plowed to a greater depth ; 

 and where crest and crest aid each other 



we have that astonishing leap of the water 

 which breaks the cohesion of the crests, and 

 tosses them shattered into the air. The phe- 

 nomena observed at the Whirlpool Rapids 

 constitute, in fact, one of the grandest il- 

 lustrations of the principle of interference. 

 TYNDALL Lectures on Light, lect. 2, p. 57. 

 (A., 1898.) 



3715. WAVES OF HEAT LIKE 

 WAVES OF LIGHT Ethereal Billows Beat 

 on Human Body. To the eye of the phi- 

 losopher, looking at such matters without 

 reference to sensation, these obscure radi- 

 ations [of heat] are substantially the same 

 in kind as those which produce the impres- 

 sion of light. You must, therefore, figure 

 the molecules of the heated body as in a 

 state of motion; you must figure that mo- 

 tion as communicated to the surrounding 

 ether, and transmitted through it with a ve- 

 locity which we have the strongest reason 

 for believing to be the same as that of light. 

 When, therefore, you turn towards a fire 

 on a cold day and expose your chilled hands 

 to its influence, the warmth which you feel 

 is due to the impact of these ethereal bil- 

 lows upon your skin. They throw the nerves 

 into motion, and the consciousness, corre- 

 sponding to this motion, is what we popu- 

 larly call warmth. TYNDALL Heat a Mode 

 of Motion, lect. 10, p. 276. (A., 1900.) 



3716. WAVES OF LIGHT MORE 

 RAPID AS HEAT MORE INTENSE Wire 

 Passes from Red to White. A platinum 

 wire [through which an electric current 

 flows] is warmed by the current, and may be 

 felt to be warm by the hand. It emits waves 

 of heat, but no light. Augmenting the 

 strength of the current, the wire becomes 

 hotter; it finally glows with a sober red 

 light. At this point Dr. Draper many years 

 ago began an interesting investigation. He 

 employed a voltaic current to heat his plat- 

 inum, and he studied, by means of a prism, 

 the successive introduction of the colors of 

 the spectrum. His first color . . . was 

 red; then came orange, then yellow, then 

 green, and lastly all the shades of blue. 

 Thus as the temperature of the platinum 

 was gradually augmented, the atoms were 

 caused to vibrate more rapidly; shorter 

 waves were thus introduced, until finally 

 waves were obtained corresponding to the 

 entire spectrum. TYNDALL Lectures on 

 Light, lect. 5, p. 174. (A., 1898.) 



3717. WAVES OF SEA AND LAND 

 IN EARTHQUAKE Undulations Transmit- 

 ted through Solid Bodies. Mr. Mallet, in 

 his memoir [1846] . . . has endeavored 

 to bring to bear on this difficult subject 

 [of ea/thquake shocks] the more advanced 

 knowledge obtained of late years respecting 

 the true theory of waves. He conceives that 

 when the origin of the shock is beneath 

 the deep ocean one wave is propagated 

 through the land, and another moving with 

 inferior velocity is formed on the surface 

 of the ocean. This last rolls in upon the 



