749 



SCIENTIFIC SIDE-LIGHTS 



VVatev 

 \Vu\e-inotioi 



act like cylindrical lenses, introduces vari- 

 ations in the intensity of the light, and 

 materially enhances its beauty. TYNDALL 

 Lectures on Light, lect. 1, p. 36. (A., 1898.) 



3709. WATER,WONDERFUL TRANS- 

 FORMATION OF Feathery Lightness of 

 Snotc. We are all familiar with the way in 

 which the flakes, in falling, are driven about 

 by the slightest breath of air, and every one 

 knows, likewise, that a handful of snow is 

 perhaps as light a handful as one can lift. 

 The actual weight of snow depends very 

 much upon circumstances. Snow varies 

 greatly in compactness, but on an average 

 it is found that a cubic yard of this sub- 

 stance weighs about 187 Ibs., or about one- 

 twelfth of an equal bulk of water. Ice itself 

 is lighter than water, but in nothing like the 

 same proportion; and a certain volume of 

 snow would, on an average, have only about 

 one-eleventh of the weight of an equal vol- 

 ume of ice. No one will be at a loss to 

 understand the reason for it; it is so mani- 

 fest that snow in the mass consists of in- 

 numerable little spicules of ice interlaced 

 together, and having a great quantity of air 

 enclosed in the meshes, that the lightness 

 of this substance when compared with ice 

 or water will not excite any surprise. 

 CHISHOLM Nature-Studies, p. 29. (Hum., 

 1888.) 



30 1O. WATERS CROWDED UPON 



WATERS The Whirlpool Rapids at Niagara 

 Illustration of Wave - action. The most 

 impressive illustration of the action of 

 waves on waves that I have ever seen oc- 

 curs near Niagara. For a distance of two 

 miles, or thereabouts, below the Falls, the 

 river Niagara flows unruffled through its 

 excavated gorge. The bed subsequently nar- 

 rows, and the water quickens its motion. 

 At the place called the " Whirlpool Rapids " 

 I estimated the width of the river at 300 

 feet, an estimate confirmed by the dwellers 

 on the spot. W T hen it is remembered that 

 the drainage of nearly half a continent is 

 compressed into this space, the impetuosity 

 of the river's escape through this gorge may 

 be imagined. Two kinds of motion are here 

 obviously active, a motion of translation 

 and a motion of undulation the race of the 

 river through its gorge, and the great waves 

 generated by its collision with the obstacles 

 in its way. In the middle of the stream 

 the rush and tossing are most violent; at 

 all events, the impetuous force of the indi- 

 vidual waves is here most strikingly dis- 

 played. Vast pyramidal heaps leap inces- 

 santly from the river, some of them with 

 such energy as to jerk their summits into 

 the air, where they hang suspended as bun- 

 dles of liquid pearls, which, when shorik upon 

 by the sun, are of indescribable beauty. 

 TYNDALL Lectures on Light, lect. 2, p. 56. 

 (A., 1898.) 



3711. WATERS TRANSPORTING 



SEEDS Wmd and Wave Combine to Plant the 



Sedge in New Locations. The most abun- 



dant plants in marshes and by pond-sides 

 are the sedges. They resemble coarse grass- 

 es, for which they are frequently mistaken. 

 Some of them have seeds adapted to wind- 

 dispersal by means of cottony tufts of hairs ; 

 but most of them simply cast their seeds 

 upon the quiet waters, where they float upon 

 the surface and are driven along by every 

 breath of wind. It will be worth your while 

 to remove some " seed " of sedge from a ri- 

 pened head and study its structure. As you 

 pick up what appears to be the seed . . . 

 you notice how little weight it has. On look- 

 ing closer you are likely to see that it is 

 triangular, in many species being shaped 

 like a miniature beechnut. If you press 

 upon it the " seed " breaks, and you find it 

 apparently hollow on the inside. But if you 

 look carefully you will see within a tiny 

 body, which is really the seed. The other is 

 simply an air-filled boat in which the seed 

 remains. A seed with such an outer covering 

 is called an achene, altho in most achenes 

 there is not the air space which these sedges 

 show. Now drop some of these sedge achenes 

 upon the surface of water in a tumbler or 

 other vessel. Do they sink? See them rest 

 buoyantly upon the top, with one flat side 

 down and the two other sides projecting 

 upward. Blow gently across the water; see 

 how quickly the tiny sails catch the breeze 

 and the achenes move away. Fancy them 

 upon a quiet pool out-of-doors: the wind 

 ripples the surface and away they go to the 

 other side, where they may find lodgment, 

 or, perchance, if the pool has an outlet, they 

 may be carried far away by the running 

 water. WEED Seed Travelers, pt. i, p. 26. 

 (G. & Co., 1899.) 



3712. WAVE-MOTION IS THE AD- 

 VANCE OF A FORM The Particles of Wa- 

 ter Merely Rise and Fall. In the earliest 

 writings of the ancients we find the notion 

 that sound is conveyed by the air. Aristotle 

 gives expression to this notion, and the 

 great architect, Vitruvius, compares the 

 waves of sound to waves of water. But the 

 real mechanism of wave-motion was hidden 

 from the ancients, and indeed was not made 

 clear until the time of Newton. The central 

 difficulty of the subject was to distinguish 

 between the motion of the wave itself and 

 the motion of the particles which at any 

 moment constitute the wave. 



Stand upon the seashore and observe the 

 advancing rollers before they are distorted 

 by the friction of the bottom. Every wave 

 has a back and a front, and, if you clearly 

 seize the image of the moving wave, you will 

 see that every particle of water along the 

 front of the wave is in the act of rising, 

 while every particle along its back is in the 

 act of sinking. The particles in front reach 

 in succession the crest of the wave, and as 

 soon as the crest is passed they begin to 

 fall. They then reach the furrow or sinus 

 of the wave, and can sink no farther. Im- 

 mediately afterwards they become the front 



