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42 LIGHT AND WATER Fig. 17a may therefore be taken to represent the general effect of waves travelling directly towards or away from the spectator, and here the streak is very clearly defined and far too long to appear in its entirety on the greased glass. In Fig. 17c, which illustrates the condition when the waves are running at right angles to the direction of ! sight, the streak is W very short and illA defined. Thus we see that when, as is <> generally the case, one is looking obliquely at the sur> . —- . face of the water, — the action of the latter kind of waves may almost be neglected in compari_ son with that of the 3 | former. A combinFig. 17b. Glass turned round horizontally through 45°. ation of the two forms of streak, that is to say, the length of the vertical streak with the width of the horizontal one, would give approximately the effect produced if the wave-surfaces faced equally in all directions. — When the photographs shown in Plates IX and X were taken, the wind happened to be blowing hard from the north, and the ripples were travelling, as may plainly be seen, across the direction of sight. tt tire ete ee ül 8 6 gi a st f° Shee d áá d ő E ő ő ő ő ág ő a d a B ő En a d é zá a á a ka dása ge a a ő SEK a a NN A B img 2S a 2 2 2 2 & e = = = a. oo oe ose se Pees eho ‘o's ss ee “! = w eee a al eee ee a éa ű @ = e i: = @ ‘ a: = Cai fi J. ane poder: = i = Meat entre ns natatetets ez eze egkee He ti nate ete JN KEN tee! elaltatja teti te Ki "at = Ce eee ee ea HO eo ee = ma ni aon see al mS nee Fő En a. 2 © © ate + e. e e. = os a a 1 = = = “a == 8 8 = J 7 KÖR erga valt etetett al tő ana övezete oe i nator" aa sonatas Henan a te fe ee =o i a “ss a ee ma a nae = = d a a a mm . 5 8 2 = = Se) 8 2S ‘Structural
